Irrelevant, irrelevant, irrelevant detail , irrelevant detail.
Tiny bit of actually relevant info.
Scary dude.
Well, it is irrelevant for people like us who already know how a HDD works and how files get "deleted" (or, to be more accurate, marked as free space). I believe his objective is to shed some light into science for people who never had much contact with it, and he does a pretty damn good job at that, IMO. Simple concepts, nice examples, simple animations explaining what he's saying, etc...
But watching the video again, and yeah... He does talk a lot about unrelated stuff in order to make his point.
