A lot of all this is about the best ways of dealing with people and allowing them to learn rather than specifically about flying instruction. That isn't really something that's taught in the flying instructor course. It comes with experience, both of flying and of life. It also involves a genuine empathy with people and desire for them to do well...not necessarily the same as liking them, though that helps too. Not all flying instructors have this. Some are better at it than others, and some improve as they gain the experience. Some don't even realise it's important!
To my mind, anything like Confabulous describes is something of a nasty trick, and ultimately won't help the student. It smacks of the instructor trying to put one over on the student, to prove how clever he is. I don't like it and I wouldn't do it. Flying is hard enough without instructors being devious.
Instructions and teaching should be simple and straightforward. If someone forgets the whole "I have control" thing, then keep reminding them. If they keep leaving their map out of reach, then remind them till they remember. We've all done it, and Confabulous shouldn't have been made to feel bad about this. As I think someone said earlier in the thread - you learn from something and go on. Well, I think this type of trick-playing makes it harder for the student to do that. It was a little thing; it shouldn't have been made into something big and dramatic by the instructor.
Having said that, instructors are learning too. So let's not be too hard on this guy...though I still think what he did was unhelpful.