I'm not gonna interact directly with their comment, but I think it's worth mentioning that a lot of definitions include some reference to assuming she doesn't know what she's talking about. One definition is "the act of a man explaining something to a woman in a condescending, overconfident, or oversimplified manner, often assuming she lacks knowledge about the topic".

So the person above suggesting that he was never told who she was is not realizing that it's still mansplaining even before he finds out. I'm not saying you should have to believe everything a woman says, but the fact he just assumed she was as ignorant as he was and didn't stop to reflect on that, look into it, or at least ask a follow up question about her experience is part of the problem.

This article has a chart and you can see that if you're not sure of a woman's background it's probably going to end up that you were mansplaining: https://www.bbc.com/worklife/article/20180727-mansplaining-explained-in-one-chart