I don't know about stuffing, but my package sticks out like that if I pull my boxers up around it and have my cock folded straight down over my balls. Stuffing is not necessary but a few seconds of preparation most likely are.
I think Conor's real insecurity is over his height. If you ever see his old posts before becoming famous, he used height as an insult. He cuts weight to fight smaller guys and brags about being bigger. He sits up as straight as possible to make himself look taller and so on.
I'm not one for giving a guy shit about his height, and I'm no giant myself, but a guy acting like that deserves to be called out on it. He struts around like Vince McManlet.