Here's what I can tell you. As someone who uses an iPhone exclusively.

Things you google or view in Safari will be reflected in you FB feed.
Things you send/receive in your email will be reflected in Safari as well as FB.

Then it gets weird, if that's not weird enough already.
Things that you watch on TV, or things said on the TV in the background, or things that you talk about on the phone or even conversations you have with people in person while your phone is in your pocket...
Will be reflected in Safari, Google and FB.

My wife is a sheep and ardent skeptic of everything. Glp is my escape. She believes in nothing CT related. (However, this election cycle she is starting to see the light, so to speak). Point is, she has noticed this too. And when it happens, we point it out to each other.

For example, we were talking about taking a trip or a cruise. Talking about it in person while sitting in the backyard smoking (cigarettes).
She goes inside and 2 min later yells to me that she has a sponsored post on FB for a vacation company that specializes in booking cruises. Later that night, I get some spam email for discount airfare to Hawaii and other areas in the tropical regions. Then we start seeing commercials on TV for Princess and Carnival cruise lines. This kind of thing happens All the time.

It's simple algorithm type marketing. The Google God basically gives you what you want. If you're reading websites or watching YouTube videos, expect to see plenty of related content across all of your social media accounts as well as Google ads.

The one thing I have yet to confirm or prove, are the tv commercials. I don't know how specific they can target you this way. In other words, using the above example about taking a cruise. Can they send my home a direct marketing commercial? Or is it regional, nationwide or based on the cable/ satellite tv provider? Do they use info from a group within a city, state or region, then direct market specific commercials this way? Or can they market specifically house by house? I'd like to talk to my neighbors and see if they get the same commercials as we do when these specific commercials come up... But I really don't want to open that door with the people on my street. Know what I mean?

Anyway, you're seeing these things because that's what you want to see. Or so they think you do.

I won't even get into the occasional direct marketing I've noticed that is based on things I buy, where I go or sometimes, even based on the things I think about. But that all has and does happen too.