You see that kind of thing all the time like with your friend. If you're both the same bf% yet his waist is 34 to your 29 then it simply looks like he has a larger frame, bone is heavy. Also some people can be denser muscle wise depending on the way they train. All sorts of things, really rather than the sort of "pumped" muscle that can come from training with lighter weights. I'm just speculating though. I wouldn't dwell on it
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I'm always watching guys in the ufc where you'll see two guys of virtually the same height and weight and yet there will be one who looks tiny in terms of muscle compared to the other.
Keep job!