Yeah, you kinda got to the breakdown in this conversation. Google sure knows that you're using Plex.
That is not a concern, though. Plex is a perfectly legal piece of software.
I think people are taking me saying "Google doesn't know what you're streaming with Plex, but Plex does, so that'd be a bigger issue" as irrelevant because they assume Plex is itself a liability, which it isn't.
It's weird how corporate copyright assumptions have seeped to the mainstream and people assume that anything you do with your owned media is illegal unless you're paying somebody.