I don’t know how, I haven’t looked at or reverse engineered the code. What I do know is that topics I discuss with friends and family suddenly appear in the form of ads and user generated content in my FYP, when none of us has done a search or engaged in other online activity associated with them. Sometimes literally while we’re talking.

Isn't this just because they have so much data on you already?

e.g. what are 3 30 year olds in Toronto talking about this saturday? likely the drake concert, winter tires and xmas related things..

Even if your scenario were accurate, it's unlikely their data processing algorithms would pin the conversation down to within the hour of it happening, given that the schedules I keep are not fixed or typical in any way. Also, in my case for some of these, it's exceptionally unlikely given the individuals involved (a 20-something guy and a 40-something guy with odd senses of humor and esoteric interests in a romantic relationship).