I assume this is also not adjusted for the fact that American people on average weigh 50lbs+ (23kg+) more.

Yes, it’s straight alcohol consumption so people in Japan are in effect drinking more than those numbers suggest.

It's tough to compare averages across populations when the people who don't drink really don't drink. Something that takes into account number of drinks per drinking occasion might paint a different picture.

There are more westerners outside the US than inside the US.

Sure, but “far less” is clearly incorrect.

This article might be alluding to an age difference since I am in my early twenties, but I can attest that I am a weak drinker but I drink more alcohol than virtually every Japanese person I have known - only Westerners and a number of Asians such as Koreans can drink in the same pattern as me. If you are an older person then it is common everywhere for married men to drown their sorrows in bars and pubs etc...