offensive pass interference -- something telling

I may have missed it, but I don't believe the receiver protested the offensive pass interference call at the time. If true, that would be very telling. It's hard to understand how an official could imagine it. Since it was called, it would seem that the official must have seen something. It is possible for a receiver to get open with a subtle push-off that is hard to detect from some angles. Has anyone studied that play carefully from different angles?