Vettel seems to be responsible, but to me, that's a racing incident, period. Anyway, even if Vettel had been found "guilty" by the stewards, a penalty would have been too harsh: Hamilton did not lose anything and Vettel was heavily penalised when he dropped to last place. (He got lucky there was a safety car right after the incident.).
I should have said that too. Vettel made a rash mistake when he should have recognised at that point that there was an entire race ahead & his car wasn't settled, but IMO penalties are either for deliberate punts or reckless idiocy which wrecks more than one person's day. I'd not call Vettel a reckless idiot at that point, just a bit too wound up. He didn't smack Lewis hard enough to even spin him, let alone damage his car.