African Americans dissing new Africans to the Country is no different than African Americans dissing each other when an African Americans would move from the Country in the South to the Cities in the North. Most of the time it was just light hearted kidding to let the Country person know that life and culture in the Northern cities is much different than life in the Country. Most Southerners in the USA and new people from Africa usually adjust to the new culture and everything is fine.
Africans probably do it to each other to when someone moves from a small village to a large City in Africa. You just poke fun at them to let them know that life is different in the big city and the big cities have different customs and culture.