Of course it was an accident
https://www.businessinsider.com/nest-microphone-was-never-supposed-to-be-a-secret-2019-2
More:
https://www.fastcompany.com/90309781/nest-has-a-secret-microphone-google-just-forgot-to-tell-us
They claim they never recorded anything. But of course they are going to claim that, because if they had this might violate several Federal and State wiretap laws.