Obviously that would depend on the particulars of the American black and the African black in question. There could be a host of differences - they might speak different languages, adhere to different religions... they might have two different levels of education, each might hold a world-view that's completely different from the one the other holds... They might have been conditioned to think and to behave differently... They might follow different traditions and social norms, have different goals in life and each might be in a completely different economic station in life.
Just because two people come from a similar racial or ethnic background, that doesn't necessarily mean that they're going to bear a great deal of similarities to one another.
A baby born to a set of parents who are ethnically Cambodian who lives his or her entire life in Australia or Britain or Canada, speaks English as a first language and is immersed in Western culture is not going to have much in common with someone who grew up on the streets of Phnom Penh or in the middle of the jungle.
Culturally, linguistically, politically, socially, an American black and an African black could in theory be polar opposites. Skin colour has absolutely nothing to do with it, it's not a determining factor in anything.