Saying that black, white, and asian are social constructs is like saying that male and female are social constructs
I think you should take that up with all the gays, transsexuals and intersexed (hermaphrodites) out there. And even with those excepts and grey areas of gender, races is nowhere near as cut and dry and as well defined as gender.
which is patently absurd. He is saying that racial categories are made up out of whole cloth, a figment of man's imagination. This is what the term social construct means. To expect someone to believe that defies intelligent thought.
Race is a social construct, genetic races are not the same as the races as classically defined, for example there are africans negroids who are genetically less related to each other then they are to a caucasian or a mongoloid. Our assigning race based on skin color, shape of the skin around the eye, etc is not very genetically accurate.