I think the person in the best position to actually see if it was good or not was Yapp. His reaction immediately after shooting the shot dropping his cue just short of banging it on the floor and turning to the referee waiting for the call tells me that he knew it was a bad hit. I don't blame him, I don't think he was going to call the foul on himself. But his response after the shot it is really telling.
No one knows what Yapp was thinking in the moment except Yapp himself (sometimes I am not even sure what I am thinking on such close shots).
In any case, Cornerman told us what Yapp said about why he reacted as he did. Sounds plausible to me. Cornerman's explanation also sounds plausible to me.
Hard for me to believe Yapp is lying.
Raises the question: Should refs based calls on physics. Marcel has done that, with some controversial results.
I am fine with humans making the call, even if it means some mistakes.