"Ethnicity" has become a de facto euphemism for "race" in contexts where "race" is a no-no word. And because we can't talk openly about race, a lot of people don't get that there are subdivisions within blacks as there are subdivisions within whites (Latins, Slavs, Nordics, etc.).
I think you mean different tribes, they are all th' same ethnicity.
Actually, no, technically there is ethnicity variation inside africa, but still, I think "different tribe" would have been a better term to use.