I used my DVR to record the game and though the replays that were shown on TV looked as if it was a block in the back, the original, live camera shot was from a higher perspective and caught the two players earlier in the play.
They were running together and the Rams player looked at the Falcon coming to block him and turned his head at the last moment in order to try and draw the foul.
It was much like when a punter falls down and fakes being run into. Sometimes it works and some times it doesn't. The ref didn't go for it this time, but it could have been called either way.
Did you see the hold down field, with the Rams player trying to tug his arm loose from the grip of the Falcon player blocking him?