No, I mean why does it find the right reddit thread instead any of the billions of other reddit threads? That can't be trivial to do since reddit themselves don't do it well.
Gotcha. Google search ranking threads versus Reddit search ranking threads.
I’d posit that Google counts the upvotes and other signals on the thread to calculate EAT or whatever.
It was probably linked to by other websites. I've been seeing more news organizations directly linking to reddit, and I believe Google manually boosted reddit results a few years ago. You used to never see them in search results, but now they have started showing up.