I want to add one more thing. The ads weren't just for a travel destination. It would be something totally out of character for us like "Let's build a tree house and rent in out on AirBnb" and there would be ads for renting out tree houses.
- They watch how quickly you scroll through the news feed at what you pause on, even briefly.
- They have ad deals with many of the sites you probably visit so can determine many of your search terms and interests even if you didn't search those things through Facebook itself.
- They have your friend & family graph and Facebook messenger context. Even if you personally didn't say something, maybe you mentioned it to a friend at some point and they searched it or discussed it in a chat.
I have heard this anecdote many times but I don't believe Facebook is actually recording everything we say. Mostly because I don't think our phones have that kind of battery life. I do think they have data on essentially everything you do online.