I will give 3 examples of Shumway referring to rifle-built guns that were smoothbored as "rifles" or as "smooth rifles". I do not have enough time or interest for a more full investigation of the subject at hand, but you may draw some conclusions from a small sample if you like.
1) In Muzzle Blasts November 1978 in his Longrifles of Note series of articles, Shumway featured what we know as "RCA19", or #19 in his subsequent book, Rifles of Colonial America. He starts the article with these words, "This rifle...." Towards the end of the article he states, "The barrel of this piece is of the octagon to round variety, and is smoothbored, of .66 caliber.""
2) In Muzzle Blasts November 1993 in the same series of articles George featured a robust plain early rifle-built gun with some features of the Lehigh valley. He begins the article, "Good early rifles..." Later he states "The full octagon barrel is 41 inches in overall length, measures 1 1/8" across the flats at the breech, and is smoothbored at .58 caliber. It's a smooth rifle, as so many of them were."
3) In one of his best articles ever, in MB July 1996, "A Case of Lehigh Valley Longrifle Evolution", he states in the second pargraph, "The three rifles shown here....." In paragraph 4 he states, "Its overall length is 56 1/8 inches, and the octagon to round barrel has a length of 40 1/8 inches."