I don’t think he is riding off someone else’s experience. I think there was a solid reason why Bilinkas brought up RG being a Marine in the criminal trial, whether that be as a recruit or an actual Marine.
But yes, choke holds can be taught. Breaking limbs can be taught. But it needs to be taught and practiced repeatedly so that one can actually do the maneuvers under stress with speed and effectiveness, especially against someone that is much larger than you. A relative can show you a maneuver but Marines practice hand to hand skills over and over against each and earn martial arts belts. People taking a karate class, for example, won’t usually be as effective because of the lack of repetition. Marines do things over and over so it’s second nature. That’s what makes them so effective. MCMAP is a constant part of their training as well.
I think it would also be different if RG did other maneuvers but these are classic MCMAP skills.