If you work at Google, there's a very clear policy for doing any outside "work" (volunteering, an open source side project, a business, being on a board, etc.): if it's related to your day-to-day work and/or related to Google's business (which virtually anything software is), you need to fill out a disclosure form and get a go-ahead from legal.
Obviously a Google Workspace CLI is related to Google. Why would you release this without getting a go-ahead?
I'm sad that a clearly talented engineer who cares about users was fired. I wish more engineers cared enough to make things like this. But it seems like poor judgment from the engineer's side :(
(Note: I do work at Google. This is my personal writing, though. Nothing to do with my employer)