Yeah, it is. The act of mansplaining isn’t gender specific. It is about the attempt to raise someone’s status above someone else by nitpicking what they said, with often obvious facts.
The men doing it to women just seem more popular, but men and women do it to anyone.
I guess the question is who they were even talking to. Where they talking to the astronaut, or anyone reading their message. That would make a difference.
If I say: “When the sun rises…” and someone comes along to enlighten me about astronomy and how the sun doesn’t rise, that would be mansplaining and not correcting. If they talk to someone else because my words inspirerd them to think about this, then it wouldn’t.