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 :)