This might be something Eric would have to investigate. If I go to the achievements page for the game, look for the OP in the leaderboard, and then search for the name of the achievement within their profile, it does show the achievement as being unlocked on December 8th, 2022.
Also, if I go to the list of DLC for the game, it shows seven players own this specific DLC, but then when I check the list of those who own the DLC, it only shows five players on the list.