I've never found a "normal" for alcohol consumption. My dad drank a 12-pack of Coors Light a day for most of my life (yes, I also presumed he really liked peeing). My father-in-law probably drinks a beer a week. A bender for me is 3 beers... or half a bottle of bourbon. I knew two guys in college who both drank a sixer a night. One of them was unwavering. The other was in AA meetings by spring quarter.
I agree with you, by the way - their methodology for assembling their data is unclear.