A lot of the times engineers at Google will open source libraries or tools they have worked on, which go under the Google GitHub repo, but are attached with that language. This is basically saying that it is owned by Google but it is not something Google is officially supporting. It may continue to get updates, it may not. I've definitely seen some libraries open sourced from Google, that stopped being pushed externally once the primary driver behind it left Google or moved on to other projects.
If it's not officially supported, it probably means it's just one or two people that open sourced it, and it would fall on them to keep it in sync with any internal work.
Officially supported means it's actually owned by some team. They'll dedicate resources to it, meaning it will be accounted for on any project planning or resource management the management needs to do.
"Official" is mostly about who they consider the customers of the product when making a decision.
If the project is officially open-sourced, that will be taken into consideration when project priorities, re-orgs, and direction occur at higher levels. "How does this effect our commitment to the community" is a question to address. If it isn't official, then is best-effort by the people who pushed for it to go open-source.
An open source maintainer is never obligated to address your bugs / issues. However it is good open source citizenship to be clear about what level of support people can and can't expect.
Unless the open source is part of a paid offering (like Firebase CLI), it's required to be listed as not being an Official Google Product. That said, CEL is used in a number of publicly supported Google Cloud services which means that it's well supported with dedicated maintenance. Case in point, I'm the CEL lead at Google.
Google puts that on most of its open source products including both employee personal projects and projects where Google has employees whose job it is to contribute to it.
Yes, for example the Firebase Tools CLI is open source (MIT), but it does not include the waiver, because it is an official Google product: https://github.com/firebase/firebase-tools
A lot of the times engineers at Google will open source libraries or tools they have worked on, which go under the Google GitHub repo, but are attached with that language. This is basically saying that it is owned by Google but it is not something Google is officially supporting. It may continue to get updates, it may not. I've definitely seen some libraries open sourced from Google, that stopped being pushed externally once the primary driver behind it left Google or moved on to other projects.
You can actually read some of the process that a Googler will follow when open sourcing software here: https://opensource.google/docs/releasing/