Racism isn't a concept with an agreed upon definition, but I'll give this a shot. Denigrating outgroups seems to be a human universal; racism is a specific subset of this tendency where the outgroup is physically distinct from the ingroup. Generally also with racism there's some relationship between the two groups of political or economic domination, the racism is used to justify the domination. I.e. racism is generally a kind of class relationship, not just antipathy between groups.

Our concept of racism develops from European colonialism, and yes there are certain similarities between this process and the relationship of the Arab and wider Islamic world to physically distinct groups (who were often major sources of slaves), though obviously it's not exactly the same, I'm not aware of the existence of rigid impermeable boundaries such as developed in the pre-civil rights American south or apartheid South Africa.

So I can't really give a definite answer on whether these portrayals are racism or not, but I can say that the portrayals of black Africans that you describe are certainly echoed by some medieval Arab and other Muslim writers. They also show negative portrayals of the other major source of slaves: pagan or Christian slavs. I would conclude these portrayals are examples of racism as there's a similar relationship of economic domination as in the classic examples like the American south.

A famous example is Ibn Khaldun, who writes around 1377 (Muqadimmah, ch. 23):

"Therefore, the Negro nations are, as a rule, submissive to slavery, because (Negroes) have little (that is essentially) human and have attributes that are quite similar to those of dumb animals, as we have stated."

Bernard Lewis, in 'Race and Slavery in the Middle East', gives quite a few similar examples. I recommend this book to learn more about the subject, I'll reproduce a few quotes below.

He quotes (ch. 6) an Iraqi Arab author, writing in about 902-3, who writes:

"A man of discernment said: The people of Iraq have sound minds, commendable passions, balanced natures, and high proficiency in every art, together with well-proportioned limbs, well-compounded humors, and a pale brown color, which is the most apt and proper color. They are the ones who are done to a turn in the womb. They do not come out with something between blonde, buff, blanched, and leprous coloring, such as the infants dropped from the wombs of the women of the Slavs and others of similar light complexion; nor are they overdone in the womb until they are burned, so that the child comes out something between black, murky, malodorous, stinking, and crinkly haired, with uneven limbs, deficient minds, and depraved passions, such as the Zanj, the Ethiopians, and other blacks who resemble them. The Iraqis are neither half-baked dough nor burned crust but between the two."

Lewis (ch. 7) quotes Mas`udi (d. 956), himself quoting Galen, who, he says:

"mentions ten specific attributes of the black man, which are all found in him and in no other; frizzy hair, thin eyebrows, broad nostrils, thick lips, pointed teeth, smelly skin, black eyes, furrowed hands and feet, a long penis and great merriment. Galen says that merriment dominates the black man because of his defective brain, whence also the weakness of his intelligence."

And quotes another author (Maqdisi) as saying:

"there is no marriage among them; the child does not know his father, and they eat people-but God knows best. As for the Zanj, they are people of black color, flat noses, kinky hair, and little understanding or intelligence."