Yes, this is a joke. If you’ll look at the date of the post you’ll see that it was made on April 1st, as we at SCU have a long history of April Fools ‘demos’.
We are of course still working on the actual game, but Prime 2D is enormous, and requires a lot of work to make happen. This is unfortunately compounded by our insane decision to build our own game engine (a project started in 2006!) Unlike many fan projects we have decided it is best for us to keep progress out of the public eye as things can change dramatically over the course of a few weeks. We have internal milestones and planned demos, but ultimately as we are all working on this in our spare time (and none of us have any), we will launch it when it’s ready.