Well if you watch the replay in normal speed, the WR actually shuffles his feet clearly "planting" two feet on the ground before going out of bounds. But for some reason the foot contacts never really register because it needs some serious work.
The players and field are not synced like they should be. I think what is happening is that they have so many canned animations take from over the years, that it's hard to sync up all those animations to the field. Clearly, the field and the players are not really connected and the field is there just for looks.