Many people here may have missed something. From the link in the article, Facebook does listen using your microphone. They say so themselves, they say that you have to give the app permission, and that it's used to listen to say a background music or TV show. they also deny using it to target ads, but they say they do use it for other things.
now, I also remember them writing that they only listen when the app is open and a status is being written, but I'm not sure about that statement. Anyhow, the key thing is that Facebook does overtly and publicly use your microphone with its app.
We can look at the OS permissions to see what it’s doing in the background. Facebook definitely doesn’t have the ability to listen to the mic in the background on iOS unless you’re implying that Apple created a back door for them...
now, I also remember them writing that they only listen when the app is open and a status is being written, but I'm not sure about that statement. Anyhow, the key thing is that Facebook does overtly and publicly use your microphone with its app.