This is a Native American Myth common to the more Northern parts of Canada, in which a person might become possessed by a demon - The Wendigo - which was a cannibal spirit and would force one to eat ones neighbors/husband/children...
Given the nature of the long, cold and isolated Canadian Winters, it's easy to see how it arose - and for the tribes and cultures that believed in it, it was a very real thing. A great many stories and trials concerning The Wendigo appear in the early papers, news accounts and trials of Canada.
One particular version concerns the Inuit, or Eskimo, and it warned that if you met a friend while out hunting on the ice, be careful, they might be a Wendigo...
Now, dramatically, imagine: You're a hunter, working a trapline, or looking for Seals, in the long cold Northern Winter. Perpetual evening, the sun never breaking over the horizon, the brightest it gets, a late evenings twilight. The Northern Lights, the icepack, unending in all directions. Days, Weeks on the ice, filling your sled. Isolation.
And you run into a friend, and you're glad of the company, who wouldn't be after all this time here, alone, and you talk about the hunting, the fishing, and maybe you can start a fire, and sit and talk, and he's looking at you and you're a little uncertain, maybe his hunting wasn't as successful as he said, as successful as yours, and maybe, after all, he's not the same person you knew back in the camp or village...
It's got a certain resonance and appeal...the classic cautionary tale...