It seems that the leak originated from 4chan [1]. Two people in the same thread had access to the weights and verified that their hashes match [2][3] to make sure that the model isn't watermarked. However, the leaker made a mistake of adding the original download script which had his unique download URL to the torrent [4], so Meta can easily find them if they want to. [1]: https://boards.4channel.org/g/thread/9184826…
See also: https://twitter.com/Teknium1/status/1631322496388722689