He doesn't say that. He says no white people that he of knows remember Obama. He goes on to say that their are probably some black students who remember Obama at Colombia.
Well, do you know of any black student at Columbia who has stepped up and told the world that he or she knew him back then? (BTW, one fellow black student actually made a little video about his time with Obama at Occidental, and other students had said that they knew him from there as well. Does it make any sense that he'd be known well at Occidental but not at Columbia, to which he purportedly transferred?)