Deadspin has a nice explanation as to why the officials picked up the flag and gave Carolina the win: 
The back judge saw the contact between Kuechly and Gronkowski, and threw his flag. He wasn’t paying attention to Tom Brady’s release—that’s not his job—or to the flight of the ball. Two other officials came in and overruled him, declaring that the ball couldn’t and wouldn’t have been caught anyway, and that was that.
So. The entire controversy hinges on a hypothetical. Had Kuechly not draped himself over Gronkowski, would Gronk have had a shot at the ball?
What’s your call? Should the Panthers have won?Should The Panthers Have Won Last Night? by Sports Talk Florida