Well to your first question about if he meant it in the same way white nationalists do, it's complicated, but the short answer is no.

In simple terms, Black nationalism was primarily about empowering a disenfranchised community, while White nationalism was about keeping an empowered community in power.

The term nationalism was used primarily to try and propagate the idea that blacks in America were all part of the same group, despite different cultures and origins. Although many black people in America were individually different, he believed they were all seen as a monolith in the eyes of whites, and thus were united by their oppression and categorization by whites.

This is best explained in his speech "The Ballot or the Bullet", which if you really want to know more about Malcolm X's political philosophy, is the first place I would start

"it's time for us to submerge our differences and realize that it is best for us to first see that we have the same problem, a common problem, a problem that will make you catch hell whether you're a Baptist, or a Methodist, or a Muslim, or a nationalist. Whether you're educated or illiterate, whether you live on the boulevard or in the alley, you're going to catch hell just like I am. We're all in the same boat and we all are going to catch the same hell from the same man. He just happens to be a white man. All of us have suffered here, in this country, political oppression at the hands of the white man, economic exploitation at the hands of the white man, and social degradation at the hands of the white man."

http://www.edchange.org/multicultural/speeches/malcolm_x_ballot.html

It's also worth noting that Malcolm X didn't simply conceptualize Black Nationalism as separatism, but that separatism may be the only answer if blacks were shut out of white power structures. The title "Ballot or the Bullet" refers to the idea that Blacks should engage in the democratic process, in order to elect people that would govern their own communities. However, if such efforts failed, blacks should not be afraid to seek autonomy through extra-legal means.

This does not mean of course that black communities would declare independence from the U.S., but that they would erect their own community police forces, and create their own institutions.

This separatism was conceived of politically, but also economically, as Malcolm X saw that many blacks were buying goods from white shop owners and companies, and getting credit from white banks. In an economic sense, this separatism was conceived of as creating enough black businesses, that black communities could get the majority of their goods and services from black owned companies. This way, money would stay within the black community, and could be reinvested in that communities welfare.

Another quote from "The Ballot or the Bullet" illustrates this:

"Then you wonder why where you live is always a ghetto or a slum area. And where you and I are concerned, not only do we lose it when we spend it out of the community, but the white man has got all our stores in the community tied up; so that though we spend it in the community, at sundown the man who runs the store takes it over across town somewhere. He's got us in a vise. So the economic philosophy of black nationalism means in every church, in every civic organization, in every fraternal order, it's time now for our people to become conscious of the importance of controlling the economy of our community. If we own the stores, if we operate the businesses, if we try and establish some industry in our own community, then we're developing to the position where we are creating employment for our own kind. Once you gain control of the economy of your own community, then you don't have to picket and boycott and beg some cracker downtown for a job in his business."

http://www.edchange.org/multicultural/speeches/malcolm_x_ballot.html

​

In summary, black nationalism is very different from white nationalism, because black nationalism is, in part, a reaction to white nationalism. Conserving power already held, is quite distinct from erecting new sources of power. Separatism didn't strictly mean that black people and communities would create their own nation state, but merely that they would fight to govern themselves (a principle America was founded on, but that only initially applied to wealthy whites). If you want to know more, I highly recommend reading the transcript of the speech I have cited, it really captures the core of how Malcolm X viewed Black Nationalism. Additionally, its worth noting that the exact meaning of Black Nationalism differed depending on who you were talking, so this answer has dealt exclusively with Malcolm X.

​

While u/ripred42 makes a good point about Malcolm X's interest in black economic independence, I don't think it's fair to characterize his ideas merely as:

In simple terms, Black nationalism was primarily about empowering a disenfranchised community, while White nationalism was about keeping an empowered community in power.

For much of his career as a political and religious activist, believed in literal black nationalism - that black people should have their own communities and land, and that integration with whites was impossible. Many of his positions in the early 1960s, including religiously-justified racism and opposition to inter-racial relationships, are mirror images of ideas from other supremacist and nationalist groups.

His beliefs did evolve somewhat in mid-1964, just shortly before he died. For example, became less keen on the idea of a black homeland, but he remained deeply skeptical about the viability an sustainability of integration (in his autobiography, he called it "hypocritical integration").

Consider these excerpts from his 1963 interview with black writer Louis Lomax. It's rather long, so I've added emphasis to key points. The full interview is here for you to read if you're interested: http://teachingamericanhistory.org/library/document/a-summing-up-louis-lomax-interviews-malcolm-x/

LOMAX: "Minister Malcolm, we are all by now familiar with your basic philosophy; we have heard you speak, seen you on television, and read your remarks in magazines and newspapers. By now, I think, everybody knows your position that the white man is a devil, a man incapable of doing right; you hold that the black man is of God’s divine nature, that he fell from power because of weakness; you hold further that the white man’s rule over the earth was scheduled to end in 1914, but that his end has been delayed because of the need to get the American Negro into the fold of the black brotherhood."

MALCOLM X: "Yes, sir, that is what The Honorable Elijah Muhammad teaches us. The white devil’s time is up; it has been up for almost fifty years now. It has taken us that long to get the deaf, dumb, and blind black men in the wilderness of North America to wake up and understand who they are. You see, sir, when a man understands who he is, who God is, who the devil is… then he can pick himself up out of the gutter; he can clean himself up and stand up like a man should before his God. This is why we teach that in order for a man to really understand himself he must be part of a nation; he must have some land of his own, a God of his own, a language of his own. Most of all he must have love and devotion for his own kind."

"...Now, you integration-minded Negroes are trying to force yourselves on your former slave master, trying to make him accept you in his drawing room; you want to hang out with his women rather than the women of your own kind."

LOMAX: "Are you suggesting that all of us who fight for integration are after a white woman?"

MALCOLM X: "I wouldn’t say all of you, but let the evidence speak for itself. Check up on these integration leaders, and you will find that most of them are either married to or hooked up with some white woman..."

"…Men who are proud of being black marry black women; women who are proud of being black marry black men."

LOMAX: "I have heard you say that a thousand times, but it always jolts me. Why do you call the white man a devil?"

MALCOLM X: "Because that’s what he is. What do you want me to call him, a saint? Anybody who rapes, and plunders, and enslaves, and steals, and drops hell bombs on people… anybody who does these things is nothing but a devil."

"Look, Lomax, history rewards all research. And history fails to record one single instance in which the white man –as a people–did good. They have always been devils; they always will be devils, and they are about to be destroyed. The final proof that they are devils lies in the fact that they are about to destroy themselves. Only a devil–and a stupid devil at that–would destroy himself!"

"Now why would I want to integrate with somebody marked for destruction?"

"The Honorable Elijah Muhammad teaches us to get away from the devil as soon and as fast as we can. This is why we are demanding a separate state. Tell the slave master we will no longer beg for crumbs from his table; let him give us some land of our own so we can go for ourselves. If he doesn’t give us some land, there is going to be hell to pay."

"…You Negroes are not willing to admit it yet, but integration will not work. Why, it is against the white man’s nature to integrate you into his house. Even if he wanted to, he could no more do it than a Model T can sprout wings and fly. It just isn’t in him."

"Now The Honorable Elijah Muhammad says it would be the easiest thing in the world for the white man to destroy all Black Muslims. **We contend that the white man is a devil. If he is not a devil, let him prove it!"

"He can’t do it, Lomax; it isn’t in him; it is against his nature.**"

LOMAX: "Reverend Martin Luther King teaches a doctrine of nonviolence. What is your attitude toward this philosophy?"

MALCOLM X: "The white man supports Reverend Martin Luther King, subsidizes Reverend Martin Luther King, so that Reverend Martin Luther King can continue to teach the Negroes to be defenseless–that’s what you mean by nonviolent–be defenseless in the face of one of the most cruel beasts that has ever taken people into captivity–that’s this American white man, and they have proved it throughout the country by the police dogs and the police clubs. ... Martin Luther King is just a twentieth-century or modern Uncle Tom or religious Uncle Tom, who is doing the same thing today to keep Negroes defenseless in the face of attack that Uncle Tom did on the plantation to keep those Negroes defenseless in the face of the attack of the Klan in that day."

"Now the goal of Dr. Martin Luther King is to give Negroes a chance to sit in a segregated restaurant beside the same white man who has brutalized them for four hundred years. The goal of Martin Luther King is to get the Negroes to forgive the people the people who have brutalized them for four hundred years, by lulling them to sleep and making them forget what those whites have done to them, but the masses of black people today don’t go for what Martin Luther King is putting down."

"LOMAX: And you will continue to preach separation from the white man?"

"MALCOLM X: Yes, sir."

LOMAX: "Just a moment, if I may, Minister Malcolm. Now, you talk about separation from the white man."

MALCOLM X: "Yes, sir."

"LOMAX: You even take it so far as to suggest that we shouldn’t even get on airplanes and ships with white people. Am I correct in that?"

MALCOLM X: "Yes, sir, on the whole. Yes."

LOMAX: "What are the chances of Black Muslims joining us in picket lines for better jobs?"

MALCOLM X: "As I told you, only Mr. Muhammad can answer that. But let me tell you something: Better jobs and housing are only temporary solutions. They are aspects of tokenism and don’t go to the heart of the problem."

"The white man is by nature a devil and must be destroyed. The black man will inherit the earth; he will resume control, taking back the position he held centuries ago when the white devil was crawling around the caves of Europe on his all fours. Before the white devil came into our lives we had a civilization, we had a culture, we were living in silks and satins. Then he put us in chains and put us aboard the “Good Ship Jesus,” and we have lived in hell ever since."

"Now the white man’s time is over. Tokenism will not help him, and it will doom us. Complete separation will save us–and who knows, it might make God decide to give the white devil a few more years."

​