Wow first time I saw this, I gotta admit I won't look at him quite the same. Not that I flat out think he's racist, it's just you get an image of a comedian being a bit more lighthearted off stage, guess it just shows that you can't always tell what a persons like.
Way I look at it he's a professional comedian. Hecklers are part of the act, the good comedians incorporate it and can tease the heckler back in a way to make the audience laugh and keep the show going. He seemed more like he didn't care and wanted to argue back. Plenty of comedians I've seen have been heckled and turned it into a joke and kept going. Firemen don't let the first flame turn them back, boxers don't quit if they chip a nail, comedians should be ready to take a heckler as it's going to happen sooner or later.
On the other hand, even if what he said is racist, you have to understand that stuff happens at a comedy routine. Comedians make racist comments all the time, and if you go in there you have to lighten up. If a jokes made, or the comedian makes fun of you because you're fat, or anorexic, or because of skin color, it's something that happens all the time in acts. I do think it's possible the guy overreacted. On the other hand I wish I could see the full act to see if he was going down a racist act altogether, or if it just started where the video started. If that was the only comment he made, I think he should have dropped it and kept the act going. If he had been making jokes like that the whole time, and considering most probably expected a Kramer like routine, I can understand walking out. Worst tho was him walking off stage after that. People paid money to see him, and as a professional he should have kept going and not cut it short.