He’s probably on human growth hormone and testosterone replacement therapy for “longevity”. Maybe he doesn’t workout enough though, so he won’t have the overdeveloped physique of typical anabolic abusers. Just the extra testosterone and hgh can cause muscle growth on their own, doesn’t mean you get huge all over though.

Lizards actually don’t have biceps, that’s called a glusquai and Bezos’ is pretty standard for the species