Multy Legged Duck And Duckling: Is This A Sign

It is, again, reported duckling born with extra limbs. This time, it is in China. If you recalled, there was one very famous, 4 legged duck named Stumpy (picture below) in Hampshire. Similar cases, but worlds apart. These mutated ducks are from farms, has anyone ever curious why mutation happens there? Could it be anything to do with the feed? Or is it just evolution?