It’s entirely about self identification. There’s no gender policing, they just kindly ask people who start their comments with phrases like “as a man…” or “not a woman, but…” to refrain from further commenting. They don’t even delete the comments. Even still, inevitably if the post reaches the front page all the women in the comments will be drowned out by highly upvoted “as a man…” commenters. They just want to have a conversation without being shouted over.