[Jim S]

Since the pass was not in the air the only foul here could be holding for contacting a receiver who was no longer a potential blocker.
However if he said yes, your next question would be "For what foul?"
Actually the better response after he said no to your questions about what happened would be to say, "Then we really DON'T have a foul here, do we?"

You would not be overruling him at this point. He has told you that there was no foul that fits the rules and the situation, and that he has incorrectly applied the rules. As the referee it is your job then to get the correct call. Wipe it off. Discuss it later.