The open source policy described above was in place 16 years ago (I went through it to continue working on some existing projects), and I doubt it was very new then.
This is clearly something done in official capacity, during working hours, with the knowledge and support of his manager, who announced the CLI.
It says "This is not an officially supported Google product" because it's a DevRel sample/experiment, just like dozens of other Google repositories made by Google employees as part of their job.
That's because from what i gather so far it is a google repo with other tools using the same api they kept it in there since and even had it announced by the guy's manager at the time.
You know this GitHub account might be more official than I thought? Maybe the problem is more to do with their approval process, which I guess negates a lot of my comments.
Judging by the screenshot of the repo, I think most people who download this would think that it's official Google software.