Facebook for iOS uses your camera whilst you scroll your feed - iMore
The issue has come to light after a user going by the name Joshua Maddux took to Twitter to report the unusual behavior, which occurs in the Facebook app for iOS. In footage he shared, you can see his camera actively working in the background as he scrolls through his feed.
Maybe…MAYBE it’s just an unfortunate bug doing something completely unexpected, but considering how many times Facebook (sorry FACEBOOK) has previous messed with iOS (audio playing in the background to keep tracking) I doubt that this is innocent.