95% of a good paint job is preparation.
Sanding is one method to remove paint, but it’s not enough to prepare a surface for painting. Any grease, oil, etc. on the metal’s surface will prevent paint from adhering properly.
The video does nothing to stress the importance of applying successive thin coats of paint. If you want a good looking job, this is a must. If you want a “showroom finish”, intermediate sanding steps are required.
I put a written tutorial together years ago that covers these points and more: