What, so all of a sudden they're going to pull out a knife, and for what? To "own" him for insisting on checking their $50 bill? They ALREADY owned him by slapping him, and he didn't do shit back, but you still think they might have wanted to stab him too. Unlikely, but ok.
MORE likely, they're just a couple of typical ghetto chicks who go around slapping and kicking dudes and expecting not to get hit in return, simply because they're girls. That backfired on them this time, which is good. But that doesn't change my opinion that this dude went overkill. They're already down, and he's standing there laughing at them and then decides to swing a couple more times. "Oh but maybe they pulled out a knife while they were on the ground".......yeah ok......except that didn't happen, or he would have said so in court