Maybe they didn't. They could have just drained it from their own wallet to another wallet they own to troll people into working on their puzzle even though they don't plan on giving it up.
If that's what they did, seems like a very cheap way to collect the names/social media profiles/email addresses of all the people discussing the puzzle. Now somebody has a list of at least several thousand profiles who've shared tweets regarding it, sent emails to the info@ address, and can collate it against other lists of persons or pseudonyms interested in both cryptocurrency and this sort of online puzzle.
You are devious. Then execute a massive spearfishing attack.
Or use it as a hiring pool if you're an organization that is recruiting excellent code breakers.