This seems supported by the fact that the repo is not under a Google org and it has a single maintainer.
I don't think that matters? github.com/google has a bunch of projects with large warnings that "This is not a Google project", not sure why or how that is. From the outside it looks like if you work at Google, they take ownership of anything you write.
That is precisely how it works.
Disclaimer: I am not a lawyer, and I'm sure the validity and enforceability of the relevant contract clauses varies by jurisdiction.