There's a difference between awareness campaigns and click / conversion campaigns and if there's some ads for a garden chair and your friend is sitting on it you'll definitely remember it more than some random model. Or clothes that are advertised on your body. Not saying that's the future we want, but it would definitely work for a while.
I'm sure the real reason is that Facebook added a poorly thought out feature to their marketing tools around that time, and someone just decided to try it out.
Sometimes people really miss the forest for the trees. Most people actually like Facebook. If you can't wrap your head around that you have to accept you are distinct from the typical consumer. A trillion dollars is not made by appealing to the margins. If Facebook really sucked so bad everyone would log off.
Instead of another boring Facebook sucks comment why don't you ask your sibling why they didn't stop interacting with the website after that? You would probably learn more about the world doing that than trying to speculate about marketing tool features at a company you don't work for.