But you aren't being recorded or listened to. Countless security researchers have dug into this problem and can tell from the traffic that there is audio being recorded. Furthermore, if facebook is accessing the microphone without permissions, it would be through an unknown security vulnerability and would be against the terms of service with both android and ios.

You are just not noticing these ads until it is something you have called out. You would never have given a second thought to this totally random item otherwise.

I have tried the same test as you multiple times just for kicks and have never found it to be confirmed.