"Space was a set of cells, each with eight neighboring cells," <-- do you really mean that equestria is 2d? Because cubes have 6 (or 26) neighbors and octahedra don't tessellate.

That was my first thought as well, but there are a variety of ways to make it work. Still, given that he only needs 6 possibilities when finding the block of ruby, I guess "6" was meant there.