Another look at steamdb today revealed the truth. You can see screencaps showing three people playing the game at the same time, and steamdb has a graph showing activity throughout the week. It is highly doubtful this is the work of fans who hacked into the game. These are the developers, or at least playtesters.
GenreAction
Platforms pc
DEVELOPER Rocksteady Studios | PUBLISHER Codemasters | RELEASE DATE
Batman: Arkham Knight Reviews pc