Ari Grant, engineering manager at Facebook, has posted an explanation of where the iOS app was going wrong:
The second issue is with how we manage audio sessions. If you leave the Facebook app after watching a video, the audio session sometimes stays open as if the app was playing audio silently. This is similar to when you close a music app and want to keep listening to the music while you do other things, except in this case it was unintentional and nothing kept playing. The app isn’t actually doing anything while awake in the background, but it does use more battery simply by being awake. Our fixes will solve this audio issue and remove background audio completely.
This is a rather curious bug. My understanding of the media APIs in iOS is that they will suspend operation when the app is backgrounded unless explicitly told to keep running. Perhaps Facebook’s iOS app was set up in such a way to allow audio calling before that feature was subsumed by the Messenger app — this would make removing background audio a no-brainer decision.
Whatever the case, it’s not working for Nate Boateng.