I’m nonbinary femme. I don’t like masculine or male terms. A few days ago, I was on a group chat with someone and they said “this guy” and used “he/him” pronouns, not knowing my gender. I, however, told them not to address me as a guy and that I preferred neutral terms but was fine with feminine terms as well.
If they don’t know, they don’t know. You’re not the asshole.
I will say though, if your user name there is the same as it is here “SonofaBixcuit”, I would have likely made the same mistake.