There absolutely is a test environment, it was absolutely reviewed and Google has absolutely spent Moon-landing money on testing and in particular static analysis.
This is a dumbfounding level of mistake for an organization such as Google.
In addition it looks like the code was not ready for production and the mistake was not gating it behind a feature flag. It didn't go through the normal release process.
I don't think "completely untested" is correct but tested way below expectations for such structural piece of code is a lesson they should learn, it does look like an amateur-hour mistake.