I went to the NFL site (http://www.nfl.com/videos/nfl-hq-videos/09000d5d81646cea) and reviewed the play second by second. (Pause the player and drag the time using your mouse or track pad; you can do this on the YouTube copies but the NFL site gives better control.)

Here is what the video shows:
21 seconds – receiver hits the ground
22 seconds – receiver bobbles the ball
24 seconds – receiver has regained control of the ball
25 seconds – defender hits receiver on leg
26 seconds – defender kicks ball out of receiver’s hands

At 25 seconds the receiver had contacted the ground, had control of the ball and had been touched by the defender. Play was dead with receiver in possession of the ball and ball was over the goal line.

Reversing the call on the field was the correct thing to do.

If the defender had kicked the ball loose before touching the receiver, it would have been an incomplete pass. That is not what happened.