I don't think this is correct. At least not on the P2+. I can't say what happens with the P3.
My understanding is, the aircraft's software knows where the home point is and it knows where the monitor is, since both have a GPS location. The proof of this is Phantom's RTH ability and Dynamic Home Point ability. Right? The home point doesn't generally move, but the monitor will move if you walk around or bike around or whatever.
So when the Litchi software tells the Vision to locate itself near the monitor (smart phone or Android or iPad), it can do that because it knows where the monitor is and it knows where itself is via GPS. So once Magic Leash (or Follow Me) is invoked, the Phantom ignores the control signal and begins to position itself near the monitor (RTH works similarly, it ignores the control signal and flies to the home point). As the monitor moves, so does the Phantom. The controller is not involved. So technically you can walk or run or bike around holding your monitor with no controller and the Phantom will follow along. But it wouldn't be wise, because if something goes wrong, you'd want to be able to regain control - by flicking the S1 switch down and up just as you'd gain control in RTH mode.