That Steam date is incorrect. It was released yesterday:
https://twitter.com/HatInTime/status/916003843535548416
And I don't know if that's the complete tracklist since it says "and more" in the description.
Edit: Also, Humble Bundle is the publisher. Gears of Breakfast is the developer.
Edit2: Going off this tweet, I guess the couple of tracks that Grant composed are not on the soundtrack -
https://twitter.com/HatInTime/status/915317536627085313