:The word origin is attested in the earliest writings from colonial New Spain.  Moreover, it's the etymology given by the Spanish Royal Academy, the authority on Spanish word origins.  Any resemblence to the Latin-derived words related to milling is coincidental only.  The reason mole and so many other words entered from Nahuatl is because it was the Aztecs that the Spanish conquered and studied first.  Certainly, Nahuatl words have earlier origins, probably from other languages, but that doesn't change the fact that it was the language from which the words entered Spanish. 

 :Incidentally, another remarkable etymological coincidence is the word for butterfly: in Nahuatl, papaloapatl, in French, papillon.