What was the negative consequence you experienced from that interaction (genuine)? Did you follow up afterwards to understand why someone chose both the language they did?

They were made to feel awkward in that interaction for no reason, and possibly judged unfairly.

You gotta be pretty sensitive to consider momentary awkwardness a consequence when someone blamelessly and passively corrects you.

How do you reckon that they were judged here at all? This is a level of transgression roughly equivalent to mispronouncing someones name for the first time, I can't imagine anyone else even remembering this incident aside from OP and even they may only remember because the human brain reserves 10% of its space for reliving minor faux pas.

That isn't a shibboleth because it doesn't mark you as a member of their group. It sounds like a simple preference against gendered language (or maybe the default masculine, idk).

Using the word 'head' to refer to the bathroom would be a shibboleth.

Side note: I find that preference odd because I come from a context where 'you guys' is neutral, but ultimately view it as a deficiency in the english language.