I agree.. I am not sure if i missed something in his video, but I don't think he actually explained how he controlled the height.
I would like to think the height is locked to the defined "RTH Altitude" and it will NOT go below that...
After all, If the left stick still controlls the altitude during RTH, how easy would it be to accidently bring the drone down lower than an obstruction.
So I hope its simply a case that he is using the left stick to control Yaw (which we know now works duiring RTH) and is changing the height using the RTH slider in the app...
When someone tests this, can they report back? I am still a bit too much a novice to feel comfortable trying this out myself, and even if I had a go, I am not going to get chance to fly for a while.