It could be
- a bug from the potato update
- intentional addition for the potato ARG
- using the DLC delivery/browse system to promote fanmade custom stories
I'd be surprised if it was DLC/new content for Amnesia (Re: public denunciations of an Amnesia 2), although we've only publicly seen reports of work on the new engine. It's possible the rest of the team was working within HPL2 to give us a new wrinkle of the story.
As scarecrow hinted at with his screenshot, it looks like it was implemented for the files that were downloaded when you login to the Aperture Science page from inside the game. The only other game I had with this DLC tab, but no reason for it, was Super Meat Boy, which is also part of the ARG and also has downloaded files after logging in to the Aperture Science page from inside the game.