I mean, they're both at fault, but I usually believe that the person to start violence in an otherwise nonviolent situation is the primary one to blame. The white guy shouldn't have screeched so sharply at the black dude when he put his hands on his chest--when you have adrenaline pumping that might genuinely trigger a reaction like you've been attacked. If the black dude basically says that he was startled and pushed him down instinctually, that'd be more understandable, but he would still be at fault for making contact to begin with. People fuming at one another should not make any sort of physical contact. The white student DEFINITELY should not have yelled a racial slur, but while it's funny that he was chased, nobody should ever have to fear for their safety because of something they've said.
They're definitely both at fault, however the black student far more so. If I was the principle I'd initially only suspend the black student (because yelling at someone not to touch you isn't a suspension worthy offense)--but once he began to fling racial slurs, they were both liable for suspension.
I might be overbrown townyzing a situation that is genuinely hilarious. Really anticlimactic though. I was secretly hoping for a full-on beatdown (not that it would've been right).