You hit the nail on there head there. A snap action should not pass judgement on a person as a whole. Because they made a fool of him in front of a live audience, his reasonable judgement was put to the side to find something hurtful to strike back and it's always the most obvious thing. In this case it was being black. It could have been homophobic, fat, bald, ugly or many other things.
Bad choice of words? Yes.
Racist? Unproven.