the butt of the gun isn’t being braced by his shoulder, so when he shoots it the recoil is going to make it fly backwards and out of his hands

You’d be surprised how little recoil there really is with 5.56. It’s a bigger priority to get solid cheek weld and keeping the head upright which often means that most of the stock is not actually in contact with the shoulder, just the corner.

Some setups will even just have a pad on the buffer tube, or they’ll use a brace that isn’t meant to be shouldered.