He did not impede the receiver, good no call.
He pushed the receiver’s shoulder as the ball arrived.
What makes it seem like PI is the fact the defender had his back to the ball, usually a ref will assume PI on the basis of that alone.
If the ref didn’t throw the flag, I don’t think there is any issue, at best it’s a 50/50 call.
But I have never seen a PI flag picked up, unless it was determined that the ball was tipped beforehand.