Oida! You’re not only a pedant, but you’re also not parsing properly. Are you misunderstanding me on purpose? Here I am, referring to the Steinkrug (which your 1920’s source could have meant, and merely took poetic license by dropping the “krug” part), and adding a by the way about the Keferloher because I think it’s a nifty bit of trivia. And you get all hung up on the addition?
Well, my original point was (and still is) that no native speaker calls a beer mug “Stein”, and then I got curious as to where this came from. Especially as I usually hear Americans use it; Britons not so much.
Anyway, I found this on Jimbopedia: