quick little drill as to why you should have it on the thumb pad and not your palm. with your bow hand relaxed, push on it with your right knuckles - its easy to move around. Now try and do that pushing on the thumb pad - much harder since the thumb pad is in line with the forearm bones. seems to me like maybe he is shooting with an incrediibly low wrist grip. Try almost lining up your thumb pad and forearm in a straight line. You'll also move your elbow out and keep your arm away from the string.