The stories were found in virtually every nation where the ice was deep and didn't melt. They were old enough for their origins to be forgotten, but picked up in popularity from time to time, usually in response to social change; a person, frozen in ice for decades or centuries, wakes up and is shocked by how the world had changed around them. And even allowing for the remarkable capacity of both the human brain and of human societal revolutions, none of the protagonists of these tales could be nearly as shocked as the Mamoswine who inspired them, who came from a time when ice covered most of the land and humans had yet to conquer the wilderness.
Modern pokemon have acquired a respect for Man's power, having learned the hard way to avoid provoking them and to stay away, lest they risk capture – or worse. Extinct pokemon such as Shieldon or Cranidos are revived in modern laboratory conditions and handled with special care, and their descendants – wild or feral – soon adapt to the modern ways. But in Mamoswine's time, humans were not yet apex predators, and a whole band of them, with only arrows or stones as weapons, was typically unable to take a single Mamoswine down.
The Mamoswine who have thawed out, a small trickle throughout human history, maintain all their memories, including their perception of humans. Typically, they have caused great devastation before being hauled down and either killed or transported far into the wilderness – less out of compassion than because before gunpowder, their thick hides made it very difficult for humans to kill even an unconscious Mamoswine.