It's not really so much about the pixels being square as the fractal-ish nature of mordern pixel camos that result in a "scale invariance" effect. There's details and contrast at the level of the small pixels, and there's details and contrasts are medium levels, and then again at large levels. Previous US army camo mostly had detail at only one scale level.
As jcranmer says, there's more details on the reasons it works somewhere down in this page, https://www.hyperstealth.com/US4CES-ALPHA/index.html