This is fascinating, and there's a key inconsistency in the article that points to an unresolved mystery.
The author posits that sweet potatoes and tobacco moved into the highlands through intermarriage. Yet he later acknowledges that genetic evidence suggests no mixing of the highland people with the coastal people. So to me the mystery remains of how those crops got there.
"So the plants crossed over and started moving east along the coast and up into the interior. Beyond that point, there were no merchants. But when a woman married into the next clan over, she took cuttings from her family’s garden with her."
The key phrase is "Beyond that point", where that point is up into the interior where there were no merchants. That's when marriage took over.
The author posits that sweet potatoes and tobacco moved into the highlands through intermarriage. Yet he later acknowledges that genetic evidence suggests no mixing of the highland people with the coastal people. So to me the mystery remains of how those crops got there.