when shooting the semi I kept trying to use the same thumb placement or hold as I do on my bolt. It won’t work because of (like you said) stock difference. I didn’t realize the difference until I got behind the semi.
My bolt has a manners stock, resting shelf for my thumb,
The semi just has a grip so I was holding my thumb in mid air and it felt weird,
So I gripped the handle as one should and it felt a lot better. As for the video I felt he was being dramatic but maybe to help some understand.
Iv got to learn different techniques to shoot this rifle correctly.