I don't think I'd even give it credit for "solid insights"; Jacopetti and Prosperi were notorious for misrepresenting the sourcing and authenticity of much of what they shot in their films, and I don't think can be seen as reliable in any respect.

But I think you can go ahead and credit that Nicholas Olenga said what he said and put it in its context and think about it accordingly. You have to remember first the wildly complicated geopolitical tangle of things happening in Eastern Congo at this point--Lumumba's been assassinated (with Belgian and American involvement), Dag Hammarskjöld's plane had crashed and the UN involvement in Congo has been incredibly confusing, Christopher Gbenye and his allies are contesting the authority of Kasa-Vubu and Mobutu over Brazzaville and everything east of it, Pierre Mulele has returned from training in China, the Soviets and Chinese are backing the Simba rebellion in the east, Olenga is working with Christopher Gbenye while Gbenye's political ally Soumialot has his own forces and Laurent Kabila (the same man who would eventually overthrow Mobutu many years later) has yet another force under his command. The CIA eventually picked another group of fighters to back in order to fight the groups that they saw as Soviet or Chinese proxies and supplied them directly and indirectly. And there are (famously) white mercenaries operating in the entire theater as well--one unit of which would eventually claim credit for killing Olenga.

In that environment, imagining that you might actually carry out a mission that would directly attack Americans in some sense seems less like a fantastic, unreal ambition and more plausible in some respect or another--distinguishing white mercenaries or CIA proxies from "Americans" or "Belgians" is in some sense a more complicated thing than we might imagine, especially in the middle of this whole situation.

But you also want to think in the context in several other ways. First, almost all the armed groups in eastern Congo from 1963-1966 or so invoked much older historical visions of conflict against broadly conceived white, European, colonial forces going all the way back to how local communities fought against the relatively heavily armed forces of the slave raider Tippu Tip in the 19th Century--also contexts where a literal sense of who they were fighting was often a very complicated question from the local perspective. If you're fighting Frederick Lugard and the Africa Lakes Company where Lugard is basically a mercenary but is claiming to act on the authority of the British government while working for some Swahili merchants opposed to the newcomers while also doing some slave-raiding for the merchants, you have a really complicated situation where you could plausibly think of yourself as attacking "the British" even though that's not technically true. You can see the deep roots of what Olenga and his peers were invoking--the Simbaists broadly speaking did a lot of the same things that earlier uprisings like the Maji-Maji rebellion against German colonial rulers did--water blessed to protect fighters from bullets, etc--the social scientist Ato Kwamena Onoma talks about this aspect of struggles in East Congo, and others have noted that a lot of these practices continued to shape the cultural lives of insurgent groups into the major struggles in East Congo that followed the Rwandan genocide.

There's also a dimension to Olenga's bravado that resembles the same kind of attention-getting hyperbole that Idi Amin honed almost to an art form--a sort of anti-Western or anti-American braggadacio--and also feels a bit in line with what you might think of as a pan-Africanist millenarianism that popped up all around the world in the 1960s and early 1970s, a vision that local revolts against the West or against white authorities were joining together or would lead to a global-scale confrontation with white power. That's also an older metaphorical or allegorical framing in a lot of anti-colonial struggles in the late 19th and early 20th Century--Robert Trent Vinson's book The Americans Are Coming! talks about this in South Africa in the early 20th Century, that sense that Blacks somewhere else would soon be coming to the aid of embattled or oppressed African communities and vice-versa.