To PG's credit, he has an uncanny ability to pluck out relentlessly resourceful founders (self-fulfilling prophecy and all that, notwithstanding) who have greater chances of outsized success. And he's been more right about startups than almost anyone else. When he praises those founders, it often comes off as an exaggeration, but I am convinced he is being thoroughly honest.

  "As someone who went through YC and met PG while he was still actively running it, I can tell you that at least in our batch he was 100% spot on about who was going to do well. He had a tendency to spend his free time with the same individuals who ended up doing phenomenally well. It would be easy to be dismissive about this and say something about doubling down on his best investments, etc. But during our batch many of those companies had not yet become the clear cut winners that they are today, and instead only turned into them a year or so down the road."

There's a causal relationship here, but it's not obvious what direction it points.

TBH the obvious conclusion of the causal relationship seems more likely than what you are implying.