I *think* what luke is saying is depending on which side the leader falls, he rotates his body to that side to keep the belay device oriented in the correct direction. "Hang on left foot" means he pivots on the left foot and rotates the rest of his body to the right. At least that's how I read it.
You understand it correctly, probably had to do it on a climb yourself. Thank you Danf
The discussion about the kind of device that sneoh talk is discuss in the fifth edition of mountaineering and present the theory a lot better than what we can have actually.
The discussion of the video is: Do you want a shorter fall with a pro at the belay and the risk to broke the belay or a longer fall with more chance to keep the belay safe?
In the introduction of the article Will gad said: "Whenever I use a “safety” system I ask what that system is supposed to do, and how well it will do what I want it to do, and what the limitations are."
Will Gad talk about the belay and using a sling as a first piece on the upper protection of the belay. Not knowing the forces generate on the belay in the case of a factor two fall and saying that it is out topic is not knowing what that system is supposed to do and it is poor understanding of how well it will do.
It is basic knowledge, in mountaineering freedom of the hill, to know what happen in the case of a fall and how the protection interact together. I admit that it is more important in trad to know all that theory because some anchor is made with stopper of different size. As we are in the section of trad, I think that the thread of all was Hijack. The hand grip with a munter hitch is not very important and many good climber decide that they prefer a device with more control. But at first you have to know what his the hand grip!!!