Begging your pardon, but it is most definitely a WH's decision, or at least he's involved in the process, being in close proximity to the play. I've had a couple of times when, as WH, I thought the pass was backward, but my wing blew it dead and called it incomplete. After consultation with the other wing, (not a timeout conference or anything like that, just a quick, "Hey [other guy] did you have that backward?) I made the decision not to overrule my wing. If the other wing had replied, "Yeah, that was definitely backward," then it would have been on me to make the decision to rule it an inadvertent whistle.