They don't say that and that doc doesn't even mention traction. And, amusingly, it points to Dropbox's application as example of how to apply. When in reality it was due to traction on HN that Dropbox got into YC, Drew Houston was a solo founder so likely would've been rejected again on the basis of being a non-great founder since he hadn't even convinced anyone to join him.

Of course, one can always claim that "great founders have traction" but that's an obvious cop out.

This isn't malicious or bad. It's just an example of the common problem where people's view of themselves is different from their actual behavior. Something all founders should learn. It applies to users just as much as investors.