I think he may be implying that it is easier to handle the lower levels of social interaction (with friends/family) that come along with working a lot of hours if you're more introverted.

Which has nothing whatsoever to do with whether a person is overworking himself or not.

I'm introverted. There is not and has never been any meaningful connection between that and my limits with respect to working hours.

Exactly. My socially needs are rather low, so going for dinner with friends a couple times a week and having random small talk between the lectures are enough for me :)