Sorry for late response, one of the other commenters got it but if you didn’t look it up after you probably don’t know the scale of the search. There are a ton of Easter eggs and a few UFOs hanging around in the game, leading many to think there is a large scale mystery that can be solved. Also hard to describe the Easter eggs— there was a mural on a mountain, an ingame serial killer, a ghost and her daughter, a cult, ingame rumors of UFOs, an alien frozen in ice, three UFOs hovering and one crashed, and a lot more that I probably can’t remember.

So for years people scoured through the game and decompiled code hoping to find it. The search is actually vaguely still ongoing apparently, even after the leak since it takes time to parse through.

While there is still stuff undiscovered, it’s most likely that this was part of the cancelled single player DLCs. Which does suck because it was a genuinely interesting idea and it would’ve been cool if R* had managed to hide a real massive subplot in the game.

Not the best summary cause it’s been a while and I was never that invested, but it was pretty interesting in the first few years.