Interesting play here and a more interesting discussion but I've got DPI with this specific set of circumstances. The way I read the original play the defender who is 20 yards +/- down field intentionally positions himself in the path of the receiver who is tracking the oncoming pass and then simply stops making no real attempt to play the ball or the receiver, just intentionally get in the way as the ball sails overhead. The mere fact that he is stopped does not IMHO mean that A "created" the contact. I would agree that you need to see the actual play to better judge who "caused" what here but I'll flag this one for DPI.
For example, if he had just stopped but was actually covering a different A receiver as he gets run over, or if the A receiver extends his arms and "blocks" him out of the way I might have a OPI call but not on this play. And I really don't think that the case play helps us either way here.