We'd known for a while that if you bring up wolf cubs in a domesticated setting, you get an animal that looks and acts something like a dog but is much more dangerous. You lose thousands of years of selective breeding for domesticated behavior when you bring in the wild wolf genes.
Still true, but it apparently doesn't have to take thousands of years to go a good bit of the way from scratch. Thirty to thirty-five generations did the job in the silver fox case. They even look a lot different.