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.
You are not the asshole. Maybe you could’ve been slightly more polite about it, but that’s honestly looking for a nitpick.
Assuming good faith, some people will need to be educated about these things before it becomes normal and comfortable for them, and unfortunately that education will be up to you more often than you’d like.