This is Craig Wright, pretending to be Satoshi again. Apparently, he managed to sign a message with Hal Finney's private key, somehow. (Edit: or he might've pulled up an old Hal Finney signature)
The scuttlebutt is that he signed it in a non-standard way, kind of like when he "signed" a message as Satoshi to convince Gavin that he's Satoshi.
This is the real mystery, the @satoshi twitter handle "Joined May 2018". How in the world did squatters not nab that one earlier?
And yeah, without a publicly released signed message signed with the private key from block 0, he's not Satoshi. It's that simple.