ENTP girl remembered my (INFJ/m) random marriage joke a year ago

So I’ve known this ENTP girl for almost two years now, and she recently brought up a joke I made about us marrying each other (which I didn’t even remember making) while we were having our usual conversation/catch up, we talk almost every other day and I was dumbfounded since I was just updating her that my cousin is finally getting married, while she gave me news about her family/friends too.

I looked up our conversation history later that night and I DID make it in passing waaaaay back, I’m wondering now, how do you guys assess what information to retain or forget?

I’m just surprised that out of all the random things we talk about almost everyday, which she often forgets, she remembers me saying that I’m going to marry her