Any projects that does not have official headcount gets that tag line. Even some projects that are funded internally, may get that moniker externally as there's no guarantee it will be maintained.
Most of the time these are projects that individual engineers go through the pain of open sourcing.
I'm talking open source here. When it's funded, there will be people to help fix issues and put out new releases. This includes things like Go, Flutter/dart, k8s, and others.
Yes, any of those could be defunded at any moment if it was no longer advantageous for Google to support it, but for now, they are getting support and new releases.
Most of the time these are projects that individual engineers go through the pain of open sourcing.