That specific badge is for game ownership. I believe it's possible for games to be added to your account automatically in some cases (like an HD version given out for free to existing owners) which could unlock the badge without user intervention.
>or could this person have shared a steam account?
Definitely possible as well.
https://steamcharts.com/app/464350
Hopefully, the developer still has logs and data for 2018 and earlier
The community- with the admins- put a lot of work into trying to figure this out. I lead a group who does analysis of other people's codebases by scraping data from the game, as a way to identify unique codebases (and players who use open source bots). The admins went through logs and we all poured through the game history looking for anything that might match up.
The problem is that it looks like he may never have played the MMO. Besides having the shared server the game is also open sourced. It's extremely common for players to run either in the simulator or on their own private server while testing out their codebase. Looking at his journals (and a journalist did share copies of everything they had with us) I really feel that he was in the early draft phase thinking about the game but not actually playing yet on the shared server.
It’s great though how both the developer and community came together to help ID the guy.
But it also says that one friendship is just 280 days old or something.
Edit: I know that folks thought this was a red herring. Checked the steam profile, power player badge was unlocked on 10/23 but Recently Played shows nothing (might be privacy settings) and last review was 3 years ago. Do badges ever auto-unlock, or could this person have shared a steam account?