It happened to me at work recently. I thought this was fake too but my zipper broke on my backpack at work while my coworker and I were walking down a long hallway between offices. We spent the whole walk talking about backpack zippers. When we got to the other office and I looked something up on facebook I had ads for backpack zippers. It was so creepy and neither of us had searched for anything between the conversation and when it showed me the ad. Listening to my mic while I wasn't even in the facebook app was literally the only way they could have known to show me those ads.