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.
Judging by the screenshot of the repo, I think most people who download this would think that it's official Google software.
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