I don't buy it
You read this kind of stories and it sound like Google have some kind of almost magican machine that knows all about us.
But then let's look about how it works in real life*. These are real life examples.
So I hear about how they can make real diamonds in labs, I spend some time looking it up just out of curiosity, for a couple of months I get diamonds ads while browsing.
I put up a teleobjective up for sale at Amazon's sellers market, for a couple of months a get Amazon ads for camara lenses.
I put some old stuff up for sale at eBay, while I am writing these I get an eBay ad showing articles up for sale, some of them my own.
Really, it's all so incompetent I can't buy the Google, or Facebook, all knowing stance, the main reason Google don't tell about their technology is because they are conning advertisiers into thinking they have it.
*Yes, yes, I KNOW! those of you with mad 1337 skills use ad blockers and don't know what I am talking about.