googleworkspace/cli appears to be more of a hobby project developed by a single Google employee.
And this project uses "google" in its org, so I would assume it is offical or at least lawyers are running toward the owner with lawsuits.
There is an official process where an engineer can apply to a committee to have Google waive any copyright claim. That requires additional work so if your goal is simply to publish the code as open source and you do not mind it living under the Google org, using the Google repo path is usually much faster.
Disclaimer: ex-googler, not a lawyer, not arguing whether or not the situation with copyright assignment is legally enforceable or not/good or bad/etc.