This is a mix of confirmation bias and some of the tracking they're actually doing. Audio recording/streaming/processing on this level would be extremely expens

This is a mix of confirmation bias and some of the tracking they're actually doing. Audio recording/streaming/processing on this level would be extremely expensive... and they don't even need to do it to essentially end up with the same results. They don't need audio because all they need to do is cross-reference metadata. Facebook for example: they know based on network locations and other factors if your mom spent time in the same church as your neighbor, they don't even have to utter a single word. They actually know about these types of casual relationships between people before they come up in conversation.