He wasn't referring to the distance away from the screen, but rather the size of the screen -- if you quadruple the area of the screen from 24 inches to 48 inch

He wasn't referring to the distance away from the screen, but rather the size of the screen -- if you quadruple the area of the screen from 24 inches to 48 inches and also quadruple the number of pixels then there are the same number of pixels per unit area, which means if you get a larger screen and it is too large, just use a subset of it and you can emulate any smaller-sized screen without having larger pixels.