I get the idea that an "always on" monitoring system would be problematic (even if you discarded the data itself and only retained/filtered relevant bits for a short period of time). But ... I have no other way to explain events like this.

I suppose some weird correlation of user has x,y,z and they searched for a,b,c in the past, and other users search for D, then we show D at exactly the 12 hour time they searched for it.

Yes I am aware of recency bias, and how perhaps it was shown other times without recognizing it. But it's... hard to shake that feeling, and I am (well less so now) a skeptic...

If it's anything it's like AI that's eerily creepy like "intelligence" but not it, just like this is "like listening" but isn't. Both use statistical models to do creepy ass shit.