Your friend searched for it or read articles about it @ office. You two share the same geolocation and IP address @ office. Facebook figured out you might be interested in the same topics as what others in your office are searching for. Facebook shows you potentially related articles @ home.
No audio listening required.
I'd be surprised if Facebook Product Managers haven't been doing the above. This is basic.
Facebook A/B tests all sorts of stuff, all of the time. I had 2 or 3 incidents like this happen until a year ago when I eliminated use of their app for good.
When Facebook addressed this question last year, the answer was: "[Facebook] does not use your phone’s microphone to inform ads or to change what you see in News Feed". That's not a denial.
Our devices, networks, graphs(social-and-contacts and graphs-of-graphs(-of-graphs..)), its click, scrolls, likes, visits, (+ fwe millions variables) are input to a deep-learning neural-network whoose end-goal is we-know-it.
A person's participation on internet is more like theme of movie Inception. Although dream state can be equated being on internet :)
But that's legally plausible as just monitoring phone orientation to improve user experience.
You should probably discard user initiated audio recording if available but looks doable for someone with the knowledge.
Disclaimer: I know almost nothing about reversing
Ex: Choose a hundred random subjects and assign them irrelevant, obscure keywords to speak loudly into their phones while the messenger app is open. Report back with resulting ads displayed over the following week.
conversations?