In all of the 55 mentions of "Home" in the manual, it never says anything about auto-updating Home once the drone is in flight, and Home is a very important theme for the drones automated systems. Important enough that you probably shouldn't launch without it.
The manual is not exhaustive but there are people who have observed and tested to get a better and more complete understanding of how it all works.
The trick is to understand who actually knows what they are talking about and who is just guessing or repeating what they've heard from dubious sources and assume is correct.
In the flight in question, GPS conditions were poor (despite receiving signals from a good number of satellites) due to the tree cover blocking a lot of the sky view.
It had GPS and a rough position but the Phantom was not confident of the quality of the position fix.
The recorded flight data shows this message 2.5 seconds after launch:
Home Point Updated; Home Point recorded. Return-to-Home Altitude:213FT
That was when the Phantom got its the first
good GPS position fix - the first one it was confident to use and that's what it recorded for its home point.
If the flight in question had a clear space around the launch point, it wouldn't have mattered that the recorded homepoint was a few metres away from the launch point.
That would have been close enough.
But tree cover where the home point was actually recorded meant that the drone wanted to descend into the trees.
An experienced flyer might have launched from that point and reset his home point above a clear area to prevent that.
He also wouldn't have allowed RTH to do the landing if it was in a tricky area.
Choosing a safe launch point (safe for landing) is probably more important than having the home point before launching.
Are you certain it'll automatically acquire a new Home while in flight if one wasn't available at launch? A test might require launching from a tinfoil covered box or something so the drone can acquire GPS after launch, but can't get it before launch.
I like to observe and test things.
I've had to fly from locations where there is no reception, so no home point recording and the Phantom records a home point when it gets good reception when it gets out in the open.
I've also seen flight data from flights by impatient Phantom owners that launched prematurely and their drones always record a home point soon after launch.
his position maybe isn't a bad one for a "beginner" flight class; it's just not entirely accurate. Looking for a good GPS return can help keep you from flying without a Home point, which many beginners may rely on as a safety net.
The instructor has been flying drones for years and may simply not have been aware of the systems being updated if he kept doing his routine every flight, he wouldn't have ever noticed a difference.
The home point/RTH system is just as it has always been since the first Phantom in 2013. It's never changed.
The information to unlock the mysteries is there in the app. DJI Go has been in use since early 2015 but ignorant myths are still out there and being spread.
Not understanding basics like how the drone records its home point suggests your instructor does not have an enquiring mind and is happy to repeat myths, assuming them to be correct when the evidence is easily seen in the app, flying experience and recorded flight data.
If you want myths, you'll find plenty in forums like this, but you should be getting accurate information from a professional instructor.
I would wonder what other myths he is teaching.
I think the DJI GO 4 software provides you with the option to create a new Home on the fly by saying "Home is where the Controller is" (assuming GPS on the RC - or maybe using the attached phone's GPS) or "Home is where you are right now" (using the AC's GPS).
I've been looking for an answer to that this morning, and the best I've seen is a reference to the software possibly tapping into a phone's GPS to establish that.
Here is where you can reset the home point to either the current location of the drone or the controller:
