> The other one was the time I was speaking to my brother in law, who had just paved his driveway, he said "I could have used airport grade tar, but thought it was too much" and we were in front of his Nest security cam is the only thing I can think of, but the very next morning, I'm scrolling through Facebook, and sure enough, someone local is advertising airport grade tar. Why? I didn't google this, I only heard it from them.

Option A: The Nest camera not only listened to the conversation and picked out "Airport Grade Tar" and decided it needed to show adverts about it to people, but the camera also identified you to the point it could isolate your FB account in order to serve you those adverts.

(I'm making some assumptions but...)

Option B: Your brother had done various searches for airport grade tar from his home (in order to know how expensive it was). You, whilst visiting his home, were on his Wifi and therefore shared the same external IP address, your phone did enough activity whilst at his house (FB app checked in to their servers in the background, or used Messenger, etc) to get the "thinking of buying airport grade tar" associated with his external IP address associated with your FB account that was temporarily on that IP.

I had a friend who was convinced that some device in his house was listening in on his conversations with his wife as he kept on getting adverts for things they'd been talking about buying the day before but he hadn't searched for. (But she was searching for it from their home wifi, which is why it appeared in his adverts afterwards.)