Your belief is demonstrably incorrect. So as people do not get confused, it is one and the same function, wiht two methods to trigger it. DJI refer to it as Smart RTH. In laymen terms, it is when you tell it to RTH, as against Low battery or Failsafe LOS RTH. I wont sprout the manual but it is described on p14 under Smart RTH in case anybody wants clarification.
Yes, definitely read the manual. The altitude of return to home depends on many factors, including how far away the Mavic is from you when you initiate return to home. See attachment for Safety Notices