Um, all I see is a bunch of binaries, two header files and a sample app. Just header files do not qualify as an open source project.

Yep, looks like I got it wrong. I saw the license file and just assumed the source was in the repo, but of course it's not. Alas, I do not know how to delete this submission.

It's BSD licensed, and there's also an announcement post here:

http://steamcommunity.com/steamvr