I'm a sailor, so the whip finish makes intuitive sense to me.
What you're actually doing with a whip finish is the same thing that you do when you whip the bitter end of a line.
Essentially, you are over-wrapping a straight piece of line (thread) with perpendicular barrel wraps (which is what happens each time you go around the hook with the tool (or your fingers); you're forming a barrel wrap).
After 3-5 barrel wraps, you're pulling the end of the thread into the barrel and cutting it off; leaving the barrel wraps to keep the line tightly in place.
As long as your wraps are butted up against each other; and going either forward or backward, you'll get good holding power from a whip finish; since you're, essentially, burying the thread.
I usually use a double whip finish; first barrel wraps from the eye toward the back of the head; second whip finish, from the back of the head to the eye.
You can use cement as an extra insurance policy, but unless you're tying a pattern that calls for a shiny head, with two whip finishes you shouldn't need to.
That video is great!
PS - I just re-read this post; it makes sense to me; hope it will to you....