Coyotes are like bears, when somebody says they killed a 300 pounder it can often be closer to 200. Just like fishing, etc. Exaggeration often creeps in to make a good story better. I'm no biologist and I only know New England coyotes, and anything that hits 50 pounds would be a MONSTER around here.
A trapper friend in Maine shot(actually his wife shot) a 55 pound coyote. I saw it weighed with my own eyes and the thing was enormous, especially in its winter fur. In his whole life the next biggest he or his wife had ever taken was 42 and most were 20 to 35 pounds.
If that coyote is legitimate, looks like maybe that gigantism condition like the wrestler Andre The Giant had? Or the 400# Hinkley whitetail from Maine....etc. etc,