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.

Even some other tools in github.com/google have as much: https://github.com/google/python-fire / https://github.com/google/pytype/blob/main/docs/index.md / https://github.com/google/dopamine / https://github.com/google/go-tika