This is what the case is 9 times out of 10.

Mansplaining is a thing, sure. lit happens. But I think a key aspect of it is talking down to someone. Its explaining things like how to turn on a computer or telling an engineer how to do addition.

My head is filled with mostly useless facts. I've learned that if im talking to someone about something I'm interested in chances are they'll have never heard of it or no nothing about it. So I make sure to ask things like: do you know much about x? Or have you heard of you before?

It gives me an idea of how much I'll need to explain. Ive had a few instances where someone has gotten indignant to the question. To which I normally reply by jumping right past first principles and into to the heart of it. Cue confused look.

I'm right there with you, but I can't ever seem to thread the needle. Like in your Matrix example I have had people get offended by a question like that.

More generally speaking, I think it's so difficult because a lot of people aren't actually all that interested in learning or communicating in a way where a mutual understanding of each other's base reality/knowledge are understood. They prefer to operate on their innate or learned social cues and prefer making assumptions or reading between the lines of what the other person is saying. Or in modern parlance, they just go by the vibes.

I have watched two people completely talk past each other and misunderstand the other person and yet they both seemed to come out of the conversation pleased with the interaction so many times. It's baffling to me.

In theory, asking them first makes sense, but when you're me, and your nerdy interest is in stuff like nuclear reactors and linux. You don't bother asking because 90% of the time, you either know who you're talking to, and can assume that they have a similar level of knowledge, or you assume they don't because you're pretty certain they don't and it works well 99% of the time.