Another option would be that META created a small model that could be run client-side and picked the right selection of ads to show elsewhere without even exfiltrating keywords.
Tell that to Amazon who never fail to recommend me things I just bought.
The thesis is that recent vacuum cleaner purchasers are many times more likely (than the average person) to be looking to buy a vacuum cleaner.
Apparently about 20% of Amazon purchases are returned. And most returners are looking for a replacement. Some of the replacement product research is done before the return decision is made, so you get ads even if you have not initiated a return.
As much as Amazon doesn't want you to return your purchase, they really don't want you to buy the replacement somewhere else.
It would be interesting to measure how the ad ratio changes over time. Particularly when you exit the return window, but of course Amazon will know the return-likelihood curve with much greater precision.