Watch the footage (or the above jif) again. The WR clearly has his hands on the defender first, trying to push off and create separation.
It's a close call regardless. As C2C said, the bigger issue is picking up the flag after it was thrown.
No carp, it's not a close call. Tell us all the times when the defender makes contact with the receiver with his back to the ball when a penalty isn't called. (Well, I should say called and not had it over ruled by Dez Bryant)