Something is betrayed, when this happens. It reveals something about how people think about pseudonyms. It would seem many people think of pseudonyms, in a sort of unconsidered way, as being things that don't attach to actual identities.

But my pseudonym is very much attached to an actual identity - I am very much a person, and a very distinct one, who exhibits a lot of personality, who moves freely through social worlds, with whom one can develop various types of relationship, from the parasocial to the intimate. For those who have the unconsidered assumption that pseudonyms do not refer to identities, the fact that mine does causes a category error, and causes them to forget (or maybe even never notice) that the appellation by which they know me as a pseudonym, and unsubtly one at that.

I've seen other evidence of this conceptual fault line, for instance in discussions of the threats and value of allowing pseudonymous commenters on the internet, around platform policies.