And Android, and the associated real-time bits that run underneath Android (lk? The thing that provides fastboot), and Chrome OS, and whatever internal Debian modifications they're running. Google is apparently quite capable of maintaining at least three or four operating systems developments at once; what's 2-3 more?
Just like the other tech titans. Microsoft has multiple OSes, as does Apple.
I think they are working on both. If it’s an IOT OS this one might have a radically different goal.