I never meant to say that the intern should not do such things. I just meant that it's not behavior to be encouraged on the workplace because it can have negative connotations that can hurt the social aspect of the team and/or can cause burnout which will inherently hinder productivity. If an intern wants to work 12 hours for any reason by all means let him. But if he's doing 12 hours + each and every day to basically prove his worth, there needs to be a limit before all parties come out losers in the relationship.
So we can take away one or two things:
1. His rapid maturity as a developer, and deeply expanded network came at a cost to time. If he had worked less, perhaps he would have known less people, been talked about less, and consequently had a smaller network. Also, the amount of time he put into the job might be directly related to the expertise he got out of it ("Practice makes perfect").
2. His type might just be your competition at an internship.
To be honest, while you're young spending 12 hours per day away from home isn't so bad. In high-school track, we'd regularly put in 3 hours mandatory after a 7 hour school day, then do one or two more hours if we were varsity. We were just teenagers.
Now adays, I can't imagine expending that much time on a single thing (school related stuff in this case), because I have so many competing interests but then single-minded devotion was the name of the game.