How was this not a catch? Referee Gene Steratore explains

Q. What is the rule used on the near Detroit touchdown at the end of the game?A. The ruling is that in order for the catch to be completed he has got to maintain possession of the ball throughout the entire process of the catch.Q. He was on his behind before he rolled over. If he stayed on his behind would it have been a touchdown?A. No. We don't play with the two feet or one knee or anything of that scenario. We're talking now about the process of the catch. He's catching the football, as he goes to the ground, he must maintain possession of the ball throughout the entire process. So as he continues to fall if he fell with two feet and his elbow hit the ground and came out it would be incomplete.Q. It looked like he had the ball up in one hand while on his rear end, but there was continuation?A. Well, the process was not finished until he finished that roll and the entire process of that catch.Q. How long did it take to determine that?A. We had the normal time as far as the video was concerned. We would not run it any longer.False23221488Calvin Johnson of the Lions lands in the end zone with the ball on a play that was ruled incomplete during Sunday's game at Soldier Field.Joe Lewnard | Staff PhotographerFalse