I think he just didn't hang out with everyone, half the guys in ETID at the time were straight edge so I doubt that had anything to do with it.

From some interview:
IGN Music: So how hard do guys party after the shows?

Andrew W.K.: Several people in this band are recovering alcoholics, and so there are great efforts made for them to enjoy themselves without that. There's definitely a level of care and concern that surrounds them to enjoy themselves without that, having been in jail and rehab because of that and trying to turn their lives around and trying to maintain that.

It's very important to note that no where on this album is the word alcohol or drugs ever mentioned, and there's never any instruction as to what to do to have a party. Having a party is as much eating a piece of cake as it is dancing as it is drinking as it is sitting in your room listening to music. It's whatever you want it to be. That's the most important thing to know here. No one is going to say, "You're a wimp. You're doing it wrong. A real hard partier does this."

We do what we want when we want to do it, and I'll get totally drunk and wasted one night, but maybe the next night I don't want to. That's hard for some people to understand, but I just do what I want, and I just want people to do the same. The most important thing to me is that they know that they don't have to do anything to be perceived as cool by us. As long as they're having fun, they can do whatever they want.