So after spent about an hour on the Test server (and first time in the game for over a year) to test out the new 'Wurm 1.0' features, I recognised this name identical to the old Wurm developer that logged in to my local at the starting area... Interested, I went and followed him around a bit.
(note that I crashed a few times while taking screenshots)
I don't know if anyone can log in under any name on the test server or if existing account names are spoken for...
All I can say is that he acted more or less as I would have expected him to, asking about the new features and some coding specifics (also note me talking to him in Swedish and him answering in English). He had just logged off the server before I left about an hour ago. Imposter or not? You decide.