I took saber fencing lessons for a semester and since you use only one arm that is what happens, but most you are implying he was playing with another sword, 1 in a 1000 chance he is a fencer or as the Brits say he is a wanker.
Yeah you may all be laughing but this is a disease.......... it's where one arm is supersized while the other cannot get bigger. There's a professional arm wrestler with the same thing. I don't remember what it's called.
@jamac13, clearly the general bulk of the arm is missing on his other arm too.
So either he photoshpped it, or he spends way too much time doing something with this right arm that he doesn't do with his left.....