I don't think people are calling him a hero, just that he's come out of this the bigger man, and gained more respect with the public while Smith lost it.
I'm legit curious what you think Rock should've done. From my POV, if he attempted to fight back, he would've been pummeled on tv and become even more of a bitch. If he had chased Smith down and then gotten pummeled it would've been even more embarrassing.
Instead he kept his cool and continued hosting as if completely unfazed by Smith. No busted lip, no bruises, no loss in composure. It was like a "Is that your best shot? Damn that's weak." to Smith. That's professionalism.
And the fact that more people seems to think favourably of his reaction than those who don't, means that he's come out of this a winner. He's won in the court of public opinion and that's all that matters to a public figure.