"If DNA studies show these two breeds to be very close genetically, it would support the contention of mainstream historians and archaeologists that the American Indians are predominantly of Northeast Asian origin."
Why would they have been wiped out across the entire continent, other than in the isolated pine barrens, swamps and barrier islands of NC, SC, GA and northern FL, though? This region has not been free, historically speaking, of large predators, such as wolves and panthers (referred to by the Scots-Irish as "painters").
I don't know, but one possibility is that the Carolina Dogs represent the oldest canine population, in terms of residence on this continent. If immigration from Northeast Asia was continuous over several thousand years, later arrivals might have brought different breeds which either overwhelmed and assimilated any Carolina like canines elsewhere in what would become the U.S. and Canada. If the Bering Strait "bridge" during the Ice Age theory is correct, then the coastal Southeast would represent the opposite end of the continent from Alaska. Newer migrants, dog and human alike, may not have penetrated these areas in the pre-Columban era.