Remedy have started posting on social networks about an impending announcement.
You are thinking correctly, yes, this is most certainly Alan Wake 2, since they have hinted at a sequel plenty of times before. Alan Wake: American Nightmare was the last DLC released by them, and it featured some arcade mechanics and made the gameplay a bit fun and less repetitive, and Remedy could just build on that for Alan Wake 2.
Of course, this is just speculation so far, but Remedy writer Sam Lake has been tweeting that the studio has something really exciting planned for 2013. The game was released in 2010 and was treated to a weak critical and commercial reception, but the pressure on them to pull of a good game after being in Limbo for 5 years would have been big.
Sam Lake tweeted that: “Happy new year, all you lovely people! In 2013 we can finally start revealing what we’ve been up to. Can hardly wait. It’ll be cool.”
We also have a picture of their new office which is still in construction, but you probably know whose shadow that is, right?
It’s not clear whether this new game would be an Xbox 360 exclusive or will be released on the PC as well, but considering the last games came out on the PC albeit a bit late, it looks like it will be a multiplatform game.