You see both his hands. So someone else would have to use the selfie camera but also make sure they are not in frame. I mean, it's not impossible, but it's highly unlikely. As much as I would like to blame Apple products, it's more likely this is not a mirrored image but human stupidity. Seeing what's happening in the world these days, I always assume everything is human stupidity unless there's proof it's a technical error or something. Although everything Apple related is also human stupidity.