One reason for working in zones, like this, is that you're less likely to cause any smears in the areas that have been completed that would reduce the sharpness of the fine details.

For the most part, they seemed to work on center elements and then outward, which means you'd be able to keep your hand from putting pressure on sections you've already colored.

In my experience with photorealistic colored pencils like this, I preferred to work in layers, mainly because so much of getting the colors right depends on the surrounding colors, so it was easier for me when the rest of the color context was already laid. But this subject would be easier to do in zones, since the primary palette for the fur is black/browns/grays/white, so less color context is needed.

I wonder about this too. I've seen a lot of hyper realists do it this way. I suppose it's a tactic indicative of this kind of art?

Are you maybe seeing a different medium? Coloured pencils relies less on having an active underpainting than say oil paints. Plus hyperrealistic art requires a lot of pre planning so the forms move about less so painting zone by zone is more viable in a weird way. Though you can do either in most styles and mediums you just gotta adjust to your preferred workflow