Marketing move. Maybe a law suit move too, though copyright trolling is getting a hard time in the courts. IANAL though I suspect copyright only applies to code, files made from code and papers - generally expressions of ideas but not ideas themselves. For those you need a patent and those can be challenged. I suspect if Wright got serious in a legal sense then EFF might consider joining against him since it could be the status of the FOSS licenses used for most coin's-software that a copyright seeks to claw back rights from. Mr. Wright could avoid the speculation by simply transferring a token amount of BTC for satoshi's stash with a message.

tl;dr meh, stunt. Proof of Keys or gtfo