There is simply no way to know what Yapp was thinking or if he knew it was a foul. People are so certain of things, but you just don't know.
There have been many times when I couldn't tell if I committed a foul. Sometimes my mind and eyes are focused on several things at once and I don't know. It all happens so fast, and I don't get the benefit of slow mo. Nor am I thinking about physics or where a ball should go.
Sometimes I can't even remember the sequence of whether a ball hit a rail on a safety attempt. I have to rely at times on my playing partner(s) to watch closely and be the judge.
Some fouls are obvious to the shooter. Maybe even most fouls. But some are not in real time. Just as Yapp looked at the ref, I look at my playing partner to tell me: Was that a foul? Looking at my partner doesn't mean I know I am guilty.
Throw in the all the pressure of the event, and sure, I can believe Yapp truly was unsure. There is nothing in his history to suggest he knowing doesn't call fouls on himself.
