I really can't without a doubt say either way, .. I'm not in the "shut up losers it was a fumble" crowd or the "it was not a catch" crowd.
But go back and watch the 2nd video posted in this thread, and click on the play, pause, ... play, pause buttons and watch in slow motion.
It almost looks like he went down because he is reaching for the ball that had popped loose, and not because he slips.
He pops back up so fast it almost seems like he went down under control in and effort to try to get the ball, and was not falling.
I wonder if the ball would have popped out when it touched the ground if it would have been ruled a fumble or an incomplete pass.
Something to look at.