How do you know that?

[Summerthing]

Has anyone been asked how they know something factual? I mean general knowledge factual, not privileged or specialist information.
Ive been asked this twice in as many months.
The first time I was asked, I wracked my brains trying to remember where I'd learnt it (something to do with gardening).
The second time I said well it was just something I knew (something to do with pop music).
Isn't being asked how you know something quite strange? Or could there be a reason for it?
Two separate, unconnected people by the way.

Why do you keep repeating your slang phrase?

Ironically “it’s not that deep” is the most fucking stupid phrase in the English language.

"an" OP - you're welcome. I'm clever.

I've been asked it a few times - sometimes I can remember reading something, seeing it or doing it (generally somewhere off to my right in my memory), sometimes there's a convoluted trail of connections swirling around and above me where it needs to be picked - and sometimes it's just 'there', right in front of me.

Inside my head is actually an external mass of swirling information, images and things to flip through to about eight foot away. Kinda works well sometimes, although I'm pretty sure I look like a complete loon waving my arms about and looking at things that aren't there, trying to retrieve something from down the side of the cognitive sofa cushions.

I've found that different people have different "general" knowledge. So something that you know and think everyone else does, might not be as "general" as you think. Therefore other people are surprised that you know.

Either that or you come across as dumb as fuck and they are amazed that you aren't

Sometimes I know because there's a story behind me learning something. Sometimes I just know.