It was an honest mistake. It happens. I misgendered someone at the dog park about 2 weeks ago. I ment a gorgeous puppy and what I thought was his Mommy. We chatted for over an hour. She mentioned her wife. I wasn't shocked.
Then the pup with both parents came back. I made the mistake of talking to the dog and telling him that I remembered seeing him with his Mommy. I was politely and discreetly corrected. His wife, told me it was Daddy.
I was horrifled. I apologized. They both were very gracious. It turns out the "mommy" I thought was "mommy" was a trans man early into his transition. I honestly didn't know.
I never want to disrespect anyone or misgender anyone. I, like you, am from that generation that accepts all as they are and fought for that.
But nasty little kids and sneers aren't cool. Maybe I should have asked how the guy wanted to be addressed. I didn't. It felt impolite, you know, "what are you?" My bad. I should have just used they or parent. Live and learn.
Imma write about this now.