This sounds unusually stupid, even for Goggle - because they could've just poached a few engineers and it would be less risky than public, high-profile corporate espionage.
It's a core part of Sonos' complaint, I am sure you could find it in the legal filings, but this article about a preliminary injunction against Google in Germany about the same issue starts with that detail in particular: https://chromeunboxed.com/google-sonos-lawsuit-2021
"In February of 2008, Google founders Sergey Brin and Larry Page visited Space Data’s headquarters with as many as 10 other Google executives in tow"
https://www.wired.com/story/the-lawsuit-that-could-pop-alpha...
https://9to5google.com/2017/07/10/project-loon-patents/
https://www.law.com/therecorder/2019/07/29/google-settles-ip...