The Appalachian Mountains extend from the southeastern US all the way up to Canada. But the borders of what you see in the map seem to reflect the boundaries as defined by the Appalachian Regional Commission (ARC). I do think that this was a somewhat controversial choice, because the ARC is less of a cultural map of the Appalachias, but, rather, it represents a government policy one oriented around rural poverty development. So there are areas outside of the Appalachian cultural regions that sought to be included in the ARC because it entitled them to additional government money for socio-economic development. You can see the differences in the map included in the spoilers below. The darker shades of red typically being considered the cultural core areas of Appalachia.
That said, this book provides an overview for six states in Appalachia: Pennsylvannia, Kentucky, North Carolina, Tennessee, Virginia, and West Virginia. That's not every state that touches the Appalachian cultural area, as notably northern Georgis is missing, but it does cover most of the main ones. But that is clearly more than four states.
This is what it says:
So it only claims to be the heart of Appalachian North Carolina. Certainly debatable, but I do get where they are coming from, since Boone is the socio-economic center of the High Country region of the North Carolina Appalachias. (FYI, Western NC is broken up into three regions: High Country, Western, and Foothills. Me and most of my kin are from the Foothills.)
Now you claim that Boone is just "an outta the way minor college town," but that wasn't the case at all. Boone was and still is the county seat for Wataga County. Much as it says in the book above, Boone sat at an important railroad junction between Tweetsie Railroad and the Barrow & Locke trains, which connected a lot of trade up and down the Blue Ridge Mountains. This is the reason why Boone was selected for the site for a college for the purpose of training teachers for western North Carolina in 1899, which would eventually become Appalachian State University in 1967. (Both of my parents graduated from Appalachian State University in the late 1970s.
) Of course nowadays, when most people in western NC think of Tweetsie Railroad, we think of the small, but fairly fun amusement park of the same name, but Tweetsie was an important railway for the Blue Ridge Mountains until a flood in 1940 destroyed the tracks. But I can also understand if you think that it's outta the way, because nowadays Interstate 40 doesn't go through Boone, but, instead, it goes through Asheville, which is further south in Buncome County.*
By the way, if you ever go outta your way to no note Boone, I recommend going to the Daniel Boone Inn. There is a long line there, but I promise you that it's worth it for the family style meal. The food is excellent. Free refills on everything except the country-style ham biscuits.
* Interesting point of trivia: Buncome County is where the words "bunk" and "debunk" are derived, at least as the former pertains to nonsense. It's not a flattering origin. Let's just say that the House of Representatives thought that the then representative of Bumcombe County was speaking such nonsense that he may as well be speaking "bunkum."
I think that the book is not meant to detail all the interesting and lore rich parts of the Appalachian Mountains, but, rather, to represent the setting of the Old Gods of Appalachia podcast.
I agree that the map could be better at representing the Appalachian Mountains. Some places of interest in North Carolina, for example, are missing (e.g., Asheville) and some of the points of interest are slightly misplaced (e.g., Newland, which is depicted as due east from where I'm from in Burke County, but Newland's northwest of us and much closer to Boone). However, I suspect that this map may represent areas of interest for the podcast's Old Gods of Appalachia setting.