I understand everything you're saying about the radar gun even though I've never gotten into the pitch F/X stuff. (As a coach, I've always been more interested in mechanics, philosophies of pitching to hitters, etc., and use the gun mainly as a recruiting tool.) And I know the gun reads the speed well before it reaches the plate. But I usually listen intently when a scout says something, which is why I believed what he said may have caused my reading.
But, as I just posted above, my friend said both that scout and Stick Michael told him that they both wouldn't doubt that Chapman hit 103 last night, so maybe no explanation is needed.