so what that he thinks of himself as black? it's probably the race he identifies with as most. he's probably rarely, if ever, felt "white". the importance of this question isn't about genetics. many of us may find a few surprises if our DNA was analyzed. i think the point of the question is to determine what CULTURES are represented rather than what COLOR someone is. knowing what cultures reside where will help them determine what additional culture and/or language specific resources may need to be put in place.
I guess these concepts are too advanced for you.... Remember, the census does more than allocate our representatives, it also helps determine how federal funds are distributed. But I suppose if it doesn't affect you, you don't care.