Please note that I said that was my best understanding and, so, of course, I defer on that item and any others on which another person might have more thorough information. Could that distinction between "pistols" and revolvers maybe be a more modern one? Not that many people carry flintlocks these days as far as I know.
From an etymology dictionary, the meaning/origin of the word "pistol" is:
"small hand-held firearm," c.1570, from M.Fr. pistole "short firearm" (1566), of uncertain origin, sometimes said to be from Ger. Pistole, from Czech pis'tala "firearm," lit. "tube, pipe," from pisteti "to whistle," of imitative origin, related to Rus. pischal "shepherd's pipe." But earlier form pistolet (1550) is from M.Fr. pistolet "a small firearm," also "a small dagger," which may be the literal sense; though some connect this word with It. pistolese, in reference to Pistoia, town in Tuscany noted for gunsmithing.
Uncertain if that helps.