That was from the old, old oddworld.com website, predating MO. It explained the history between the gluks and muds in that the moon gave the muds a feeling of superiority and they did some less than honourable things because of this. This brought them into confrontation with the Gluks, who were an enlightened, philosophical race. The glukks attempted to use science (in their Age of Alchemy) to disprove the significance of the moon and/or actually change their own bodies to match it, until an 'accident' occurred that killed most of the glukkon race and left the rest stunted and mutated.
For more reading material, check out
TOE. Wish we still had the original wording though.
In any case, it's not clear how much of that is still regarded by owi as canon, as Lorne has hinted that the pawprint on the moon was created as Abe was escaping from the stockyards.