If you want to be double pedantic, if the iPad is controlling the controller, and the controller is controlling the drone, is the iPad not indirectly controlling the drone?
True. But that's not using the iPad AS the controller. In that situation, the app can completely crash and it will have no effect on the mission. I actually experienced this just 2 days ago on a job. The app crashed, but I let the drone finish its mission umimpeded.
And ATTI mode (AKA: The panic button) takes the drone out of ANY intelligent flight mode, INCLUDING RTH. So while your statement is technically true, it goes without saying and proves nothing regarding what the iPad is or isn't doing.
D