That study credited moderate alcohol use for long life, whereas this one finds alcohol use disorders (fancy way of saying alcoholism) is the single largest risk factor for dementia. There’s a big difference there, the difference between a glass or two of wine in the evening or with dinner, and basically crawling into a bottle and pickling your brain.
That was the way I read it as well. Moderate drinking: possibly beneficial. Heavy drinking: likely damaging.
But in neither case are they saying it’s the only factor, nor that they really understand the mechanism.