Remember when Target got into hot water for outing a pregnant teenager based on an assortment of items she bought [1]? That was based on items like scent-free soap, cotton balls, and vitamin supplements.
That was 6 years ago and (no offense to Target) done by a company that isn't nearly as adept at doing that kind of targeted advertising or inference.
For example, Facebook might know (hypothetically) that you're a young adult in the tech field who lives in Brooklyn and spends a lot of time looking at photography or you're friends with a lot of amateur photographers. So they show you ads for high-end cameras from the most popular vendors, knowing that you're likely to develop an interest in photography if you haven't already.
That's just an extremely simple example, you can imagine that there are far more subtle indicators about someone's interests or likely interests (like the cotton balls for pregnancy).
The timing is almost certainly a coincidence. It's far more likely they show you those ads all the time and you're just noticing them when the coincidence occurs because you're on high alert now for things like this.
1: https://www.forbes.com/sites/kashmirhill/2012/02/16/how-targ...