Surely it wouldnt even be required to use such story plot as genetically created mutants to introduce them. All SE really needs to say to introduce them is these moogles who may be under another name are a distant cousin to the moogle race from a far away land to the east or west or where ever. Perhaps once they too lived in a great forest filled with elementals etc but long since then that forest died and withered away. Over time the ancient language of the moogles was largely lost to them replaced by the common tongue.