Either don't schedule a phone interview after an event where you will be drinking, or don't drink at the event. That doesn't seem so hard.
>Either don't schedule a phone interview
Perhaps he didn't have the option.
>or don't drink at the event.
As others have said, networking opportunities may have presented themselves. Who are you to judge his situation with absolutely no information? Judge him on how well he conducted the phone interview. That's all that matters at this stage.
What I see are people who are obsessed with irrelevant information when it comes to hiring. Its modern-day tea-leave-reading and it has no place in what should be a rational business decision.
To some extent I'm playing devil's advocate, but you did ask for possible circumstances. I suppose in the employer's shoes I'd pretend I hadn't read the Twitter post and go ahead and carry out the interview. If he aces it, great. If he muffs it, I wouldn't make allowances for him being drunk, because he would have demonstrated showing up drunk was lousy judgment on his part.