I have noticed a similar trends, when speaking about some specific topics without following up on the device by traditional means (keyboard), ads started to show up in a day or to.

Last occurrence, 6 months or so ago, of that happening was when one of my colleagues discussed vacation in a specific place I absolutely have no interest in visiting, so I was 100% sure I didn't google it or discussed it online. Surprisingly, the next day, I was swamped with booking.com and airbnb deals for stays in that specific area.

I emphasize next day occurrences intentionally, as I am under impression that it takes some time for them to process the data and supply the results to the marketeers.