I've worked out since I was a teenager, but I've had too many injuries (two hernias, numerous nagging sore spots) and am limited by an average frame to really grow huge muscles and the possible huge ego that can, but doesn't necessarily have to, come with them. Without knowing your boys personally kls, I obviously can't tell what they're really thinking. It's possible that their size and interest in bodybuilding caused them to feel overconfident. Guys are a funny lot - sometimes, we've got too much ego and testosterone for our own good. I've seen guys checking themselves out in a mirror and admiring their body, and lord knows what they're really thinking - maybe something like, 'hey, I can take on the world'. If that's the case, then the guy is working out for the wrong reasons.
Bodybuilding can be a great way to stay in shape (there's lots of methods and not all are designed to create a monster physique) and so I think it's a worthwhile pursuit - when accompanied by a proper sense of self.