If API + binary blobs + single company control + BSD license is the new definition of open, then... hmm.
They should have called it ValveX. It's the best bad option among worse options (and that's probably why Valve won't put more effort into opening it up until the market matures), but it's not an open standard.
It's not unlike OpenGL though, which does not have a open source reference implementation either. Only the API specifications are open.
Most implementations are closed source binary blobs. Of course there is Mesa, but that is is also a 3rd party implementation. No one would prevent you from building an open source OpenVR implementation.
They should have called it ValveX. It's the best bad option among worse options (and that's probably why Valve won't put more effort into opening it up until the market matures), but it's not an open standard.