I wouldn't agree with that assertion. I frequent LH Senator Lounges quite a bit and, despite the reputation of Germans of getting naked at the drop of a hat (I have no idea if the reputation is fair or deserved, but it does exist) I have never seen any man even with his shirt off in a LH WC.

Clearly none of us know the slightest bit about this individual, whether it was a cultural thing, a bet or perhaps he was confused. However, I have noticed that many people in UA lounges simply don't know how to behave in a public space - shouting into their phones, picking their nose, playing loud music, man-spreading, you name it. This seems just like a rather extreme version of the rest of the inappropriate behavior that is commonplace in UA lounges.