It can be a coincidence. You were probably asked or talked about hundreds of things in last week and noticed this one situation.
It can be just targetted marketing, perhaps your colleague googled the book or saw the book on Amazon after getting a random ad. Ad companies understand that if someone close to you liked a product, there is a chance you will like it to so they prioritize advertising similar things to those on your WiFi/location or background.
In any case, I find it very unlikely that our devices are listening to us talk and report it to ad servers. I doubt conspiracy of level to pull it off would be still a secret. It would need to have both Apple and Google engage in it, engineers working on it would have to keep silent, it should be virtually untraceable and so on. It's just much easier to explain as coincidence along with some targetting due to ads your social circles engaged with.
It can be just targetted marketing, perhaps your colleague googled the book or saw the book on Amazon after getting a random ad. Ad companies understand that if someone close to you liked a product, there is a chance you will like it to so they prioritize advertising similar things to those on your WiFi/location or background.
In any case, I find it very unlikely that our devices are listening to us talk and report it to ad servers. I doubt conspiracy of level to pull it off would be still a secret. It would need to have both Apple and Google engage in it, engineers working on it would have to keep silent, it should be virtually untraceable and so on. It's just much easier to explain as coincidence along with some targetting due to ads your social circles engaged with.