I opened the leaderboard link provided in this post.
At the top of the Leaderboard, there is a user with username joblessperson.
I opened their Network Profile, but saw they aren't a member of SO or any SE site. The other tabs are also empty.
How is this possible? We should be a member of at least one SE (or SO) community to earn the privilege to play the Winter Bash game.
Here is their profile link.