Well, I don't know because I'm not an alcoholic.
However, it seems to me that someone doesn't become an alcoholic instantaneously. I think many people begin by drinking 'normally' in social settings. Perhaps this person was merely a social drinker but did grow up in an alcoholic household. Perhaps they only went to Al-Anon meetings a few times.
Later, when they weren't attending Al-Anon meetings and life became hard, the drinking became more regular and soon became a tool to get through the rough spots.