I studied some classical guitar as a teenager and thought all these self taught rock players had really sloppy technique. I had no idea of what was really required for blues and rock.
John

There is one fundamental flaw in that video: the guy forgets to acknowledge the fact that classical guitarists put the guitar on the left leg. That changes everything as far as left arm and hand position is concerned.
Moreover, the neck and fingerboard of a classical guitar have little to do with that of an electric guitar.

What works best on an electric or even steel string acoustic guitar would indeed be considered very bad technique on a classical guitar.

Finger length puts a limit on how guitarists interact with their fretboards. For example, people with short fingers just can’t wrap their thumbs up and over the 6th string. Take a look at John Mayer’s fingers, or Justin Johnson’s fingers. They’re 50% longer than mine.