All I can say is that, being alcoholic, I cannot have a glass of wine or a beer, ever. There is a difference between a heavy drinker and an alcoholic. The brain of an alcoholic only needs one taste of alcohol and then it's off to the races.
I wouldn't put much stock in him being able to have an occasional drink. The fact that he has to go to rehab to stop drinking pretty much proves that he cannot handle alcohol.