He may very well have given your dog beer and based on your reaction realized it wasn't the funny cool thing he thought it was at the time (while drunk). There is no way to get an honest answer out of him at this point because he knows you feel strongly about it he will lie if he had done it.
I remember in college a fraternity had a dog that the guys had given all sorts of mind altering substances to, including alcohol. I felt awful for it but it was the meanest dog (probably because of what they had done to it) and I knew if I turned them in he would have been put down and at 19 I decided to let it be. That may have been the wrong choice but it's the one I live with.
The EXABF admitted that he had forced his cats to inhale marijuana because he was alone and wanted to see how they would react. And then he laughed about how unbalanced they became. They weren't my cats and according to him he'd done it years before knowing me but I lost a lot of respect for him and told him so in no uncertain terms. He then back pedaled and told me he never did it again because he realized it was wrong. Not sure that I believe that but hopeful my reaction made him realize what a jerk thing he'd done to his innocent pets and he would not do it again.
A's are always looking for a drinking buddy. It's stupid and sad that they do this. Keep an eye on your furry friend and talk to your vet if you are concerned.