Ah, in the story it sounds like they were doing some sort of art that involved "rolling" as sparring like BJJ. But yeah fat arms take all the potential power out of punches. A good solid punch is a whipping rather than a pushing motion. The visceral fat distends their abdominals so they lose a lot out of that for being fat. Hard punches involve enlisting all of your weight to generate force, legit heavyweights can do that because they are lean. Fats tend to be more like feather weights with kettlebells strapped to their biceps when it comes to punching power.