I found mansplain on Merriam Webster, and also on Wikipedia. The Merriam Webster article says "of a man," and the wikipedia article says "for a man" at the start.

Usually for these things I'd be all for abolishing the gendered nature of the word, but I feel like it would dilute the original meaning. So if anything, instead of gender-normalizing 'mansplain,' I think we need to add 'womansplain,' which is something I'm very guilty of doing to my partner whenever he's cooking because I keep forgetting that it's something he does very well.

But also, my reply still has merit here, because that individual was obviously weaponizing 'mansplain' to try and gender me, a woman, when what they likely wanted to convey was that they found me condescending. They shouldn't be appropriating a gendered word to say something else they mean, so... uh. Sorry for all the extra words. I took my ADHD medication today and language discussion fascinates me.