It's somewhat common for people in some security circles to post hashes of messages they don't want to post publicly, but might want to refer to disclose privat

It's somewhat common for people in some security circles to post hashes of messages they don't want to post publicly, but might want to refer to disclose privately or at a later date, and have some reasonable proof they didn't make it up later. This, for example, is a throwaway account. Perhaps there's something in the message that'll let them prove they left that message at a later date, if they desire to.