The ball was jarred loose when the player went to the ground. He had not established possession and by rule must maintain control of the ball to the ground if he has not established possession. If the ball hadn't touched the ground it wouldn't have mattered if he bobbled it because he was in bounds the entire time, but, it came loose AND it touched the ground, therefore, it was an incomplete pass no matter where the receiver was on the field.
Very tough break for the Steelers, but reversing the call from touchdown to incomplete pass was correct.
Even the announcers initially got it wrong and were madly backpedaling while the play was being reviewed. The officials reviewing the play took a long time just to make sure they made the right decision on the review because it was potentially the game deciding play. Tough break, but the pass was incomplete.
The ball was jarred loose when the player went to the ground. He had not established possession and by rule must maintain control of the ball to the ground
_______
He HAD CONTROL of the ball TO the ground.