Actually Sissysnakes, it's kind of been proven that released/escaped commercial pigs will indeed become hairy, leaner, the snouts get longer over a period of months. "Domestic" pigs will go feral in appearance in a amazingly short period of time, I believe unlike most other animals.
But the "heirloom" breeds is also not quite right, since the breeds are mostly a cross between russian boar and other more common breeds, bred to look more wild.
It doesn't matter WHAT breed of pig they had. It's their legal livelihood, USDA and all. The authorities are stretching a vaguely defined term "non-indigenous" and using that to target people that they think they can get away with bullying out of business.
The government may pay "compensation" for the dead pigs, but they have destroyed the entire business, and you can't suddenly start a new business and gain income after they've taken every aspect of his income away.