I'm split on this. For one, it is 100% possible that Facebook is using machine learning to scan your conversations for keywords and use them to serve you advertising. This is completely within the bounds of modern artificial intelligence.
But also, on the internet, you are served thousands of ads per day, and most of them you will completely ignore. If you talk about something before going on Facebook, it's fresh in your mind, and you're more likely to recognize when a similar ad pops up. This is known as
observational selection bias.
Another thing to consider is that your friend who was talking about the new movie/TV show probably liked it on Facebook or searched it on Google. Facebook almost certainly uses your friends' interests to tailor the ads you receive. This is still somewhat Orwellian but far less disturbing than Facebook/Alphabet listening to your private conversations over mic.