He didn't get in.
The linesman made a bad call.
The reviewing official did not have sufficient evidence to over turn the call.
Steelers TD.
Even if he didn't get in on that play, they were going for it on 4th down and probably would have gotten in anyway.
Honestly, the Hawks' whining is nothing compared to Steeler's fans whining about the Hawks' whining.
The Hawks wouldn't have won, anyway. They were not making any plays while the Steelers were making enough plays to win.
I don't think the Steelers fans would be complaining about it at all if they felt secure about the victory. Whether they'll admit it or not, I think most of them wish they had won without so much help from the officials.