On Discord many years ago I spoke to someone about my "big belly".
The next day I received ads about exactly that topic everywhere Adsense Facebook everywhere.
So the technology is at least 10 years old and I totally believe that the story is true.
The key issue here is that we don't own our phones.
We have little control over what those apps do and often apps are hidden and can't be uninstalled.
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.
Could it be that they have the info of the holiday from your colleague. They then track the proximity between the two of you and then display you ads on things he is interested in.
You only notice these ads when it matches what you spoke about.
Well, of course I cannot be 100% sure, but I usually don't see his other interests popping up on my ads. I must say that I am the person that doesn't use ad blockers or similar tech, as I want to see what is getting advertised on which content, etc. so I think that I am more aware than the average person of what I see and why.
The holiday thing was extremely specific, it is a very small (<500 people) town in a very specific location, so unless you were not listening to our conversation and its context, it would be a very lucky guess to connect the needed dots (edit: grammar).
Nope, that didn't happen. I access Internet for personal use only on my non-shareable mobile connection. I noticed what you are talking about when I google stuff on the workplace where we share common ip.
The key issue here is that we don't own our phones. We have little control over what those apps do and often apps are hidden and can't be uninstalled.