You are not an African-American unless you are a black person who was born in America. You are not an American unless you are a citizen of America. If your parents are Mexican, I would say that you are an ancestral Mexican.
I don't know how the law works as far as being born in Africa, but I would guess that if you had to get right down to it, you are an African, at least by birth.
That really doesn't nake any sense at. To begin with you say he is Mexican but was born in Africa, how is that even possible? And no he wouldn't be African American he was just born there and if his parents were Mexican than he's just Mexican born in Africa.