Which is getting a grayscale texture of something and then try to find a perfect balance of 3 tones (shadow - base - highlight). Then this texture is going to feed the color ramp.
As for example getting a screenshot from your video, specifically on the clothes.
A proper texture painted correctly might need many hours so everything is carefully tuned, all shadows (creases, seams) all highlights (buttons, metallics) and every other detail is carefully managed.
I did this in only a few seconds trying to match the tones as best as I could, however it does not exactly looks perfect, but at least the technique shows it’s power.
As searching in google found something similar posted a while ago. It would really worth checking out.
Generally, I really like your work because that way NPR techniques are further explored and popularized. 