Gameplay mechanic:
In Elona you can breed pets, fairies being a breed-able pet.

But their statistics page often gave them weird body proportions, such as weight and height...

As an explanation:
NPC stats (at generation - you can genetically engineer your own pets yourself to change them) are determined pretty much entirely on race, class, and starting level.

As God Pets, cute fairies are "servant" race, just like the other servants (see post #1199860), and all the god pets have the same height, weight, age and basic stats as all the others. This means a "cute fairy" can be 6 feet tall and weigh 190 lbs.

Incidentally, this also means the black cat has a humanoid body, can wear plate mail and rings, and also can be generated with the same size and weight ranges.