We think of cryptography as the best way of information hiding. But it is not the only way. This sounds like some group is testing the limits of non-cryptographic information hiding. In particular, multiple possible messages encoded. How do you craft a message so that everyone is led to the decoy except those who know the secret key? And the size of the plaintext is completely hidden. Most likely this is a group associated with an intelligence agency, although they are likely not running an official project. They have an idea and are exploring it for now.

Interestingly, the NSA has access to enough Internet traffic to be able to identify people who are playing this game, even if they don't get to the final round.