I'm not sure if my guess is right but my understanding is that "mathematically perfect" is related to how close to actual crystals they are. For example the Pen

I'm not sure if my guess is right but my understanding is that "mathematically perfect" is related to how close to actual crystals they are. For example the Penrose tiling in the picture is made of tiles of 2 different types, so it's more "perfect" than another pattern that would use 3 different types of tiles, etc.