Because TC is an "authority" on the subject and people like that. Let's say that I had submitted a post about black swans at the same time as that post from PG

Because TC is an "authority" on the subject and people like that. Let's say that I had submitted a post about black swans at the same time as that post from PG was submitted, then there's a higher probability that the post from PG would reach the front page because PG is an authority