It's possible that if he only shoots revolvers, he's become used to letting the gun roll up with recoil. I can imagine doing so with an auto could cause some problems.
Yup, in my wife's
and my experience, getting "used to letting the gun roll up with recoil" can, and absolutely
will cause problems when switching to semi-autos. Mrs. .308 Norma was one of the top IHMSA revolver competitors in the state back in the '80s, and she got there with a Ruger 10.5" Super Blackhawk 44 Magnum. She knew to grip that revolver "firmly" as she put it, but to "just relax and let it buck when it goes off."
Fast forward 20 years - my wife bought her first 9mm semi for concealed carry. I think it was some model of Ruger. It jammed. Then she tried a Sig, then a Glock, then a Smith, and even a Taurus. She could make every danged one of those semi autos jam in every way that jams can occur. Yet most of them (except the Taurus) worked fine for me. So my wife went to carrying the gun she could trust - a 38 Special
revolver.
But last year my wife decided to try one more time. She bought a Smith M&P 380 EZ. It jammed for her at first too, but rather than just give up on it like she did every other semi auto she ever tried, she asked our friend (and owner of the gun range) to watch her shoot. He saw what she was doing right away. It wasn't exactly "limp wristing" but it was essentially the same thing. After running tens of thousands of full-house 44 Magnum loads in a revolver in competition, my wife had learned to grip the gun firmly alright as she squeezed the trigger, but she had developed her reflexes to the point she could immediately "just relax and let it buck" when it went off.
Since that day, I don't think my wife has had more than two or three jams with either of our semi-autos. She maintains her firm grip on them even as they go off. But she had to learn that, and it wasn't easy.
Last summer though, we both completed the Idaho "Enhanced" Concealed Carry class, and my wife put 100 rounds through her Smith semi-auto in about 45 minutes without a single failure.
BTW, running more than two or three full-house 44 Magnum loads through my wife's old Super Blackhawk is sheer torture for her nowadays. Reality is, running tens of thousands of full-house 44 Magnum loads through her Super Blackhawk back in the '80s is probably what caused the arthritis in her thumb joint in the first place.