I had an experience like this several years ago. I was having dinner with a customer, and one of the guys brought up this story about how he went to school with someone who got caught cheating on Who Wants to be a Millionaire. Later, back at my hotel, I pulled up YouTube and the first recommended video was of the guy who got caught cheating on the game show. I had not searched for this during the conversation (or prior) nor do I watch game show videos on YouTube, or cheating scandal videos on YouTube.
Here's what I think happened: somebody at the dinner googled it, and the video got recommended based either on geo-location data (we were in close proximity) or because the person who googled it was in my phone contacts, or maybe both. But, I don't think Google/Youtube was recording anyone's conversation to make that recommendation.