My son is a senior at UCLA and says the same thing - the black students from Africa are hard working, hard studying, polite, and a pleasure to be around. The American blacks mystify them, and they don’t hang around together. The Africans hang with their white/asian/indian dorm mates.
Ironically the opposite is true in Europe. Most American blacks in Europe have "found the promise land" and assimilate very quickly while many Africans come as migrant workers and don't assimilate. I tend to think tribal identities are more of a limiting factor than anything else among all races on the planet.