The charitable explanation is that they don't pay attention to usernames (I'm guilty of this too) and default to male pronouns for everyone.

The sinister explanation is that they dug through my post history, saw that I'm trans (I'm very open about it, and in fact I've been discussing my name change in another thread this morning), and decided to misgender me either out of bigotry or just to be hurtful.

I'm not sure which one to believe.