"Skentelbery" and its variants (I have a "Scantlebury" variant in my family tree) is indeed a fairly common name in eastern Cornwall. My Scantleburys originate from around Landulph and Botusfleming.
I think most etymologists agree that the "-bury" suffix gives the name away as being Anglo-Saxon rather than Cornish in origin. The Oxford Dictionary of Surnames thinks that it is simply a variant of Kentisbury, which is a town in Devon possibly meaning "Centwine's fort"--clearly very Saxon.
But that raises the question: Why the added "S"? Those who know some Cornish will recognize "skentel" as Cornish for "skilled." Could it be that the originator of this alteration of the surname was a Cornish speaker who conflated "skentel" with "kentis"? The resulting combination, Cornish skentel=skilled + Anglo-Saxon bury=fort doesn't make much sense on its own, but, in a stretch, could imply a craftsman of some sort ("skilled town worker"?).