I think this thing is completely overblown. You have to set up a GROUP FaceTime call then PURPOSELY add your own number. And this only lasts as long as it takes for the other party to pick up the call or for the call to go to voicemail. This is TOTALLY overblown.
You completely misunderstood it. You don't have to add yourself. The person eavesdropping has to add themselves, and you don't know about it. And they can even see your video. Let's say your phone is ringing, and you press the power button to make the call go away, and your camera turns on, and the other person can see everything. You don't notice that, because your screen is off, and you think you've cancelled the call. You could be straight out of the shower naked, and the camera is silently on.