How firearms are designated or classified by researchers, collectors and writers vs. how it was done during the period they were manufactured is often a problem, but not a serious one.
During the short period it was made, no changes were made in the approximately 1,100 Walkers that were produced. But after that, between 1847 and 1861 Colt made what he called the “Holster Pistol,” or sometimes the “Cavalry Pistol” in his advertising or price lists. His distributors usually used this same language. Later historians ignored what had been done, and called them “Dragoons.” That name came from the scene roll-engraved on the cylinder.
Colt often made running changes and improvements to his revolvers, and introduced them without notice or fanfare. Collectors would have none of this, and insisted that each noticeable change be specifically designated. In the case of the Holster Pistol/Dragoon there are five such classifications – all collector inspired. None of this is particularly important unless you are reading contemporary documents from the 19th century and trying to make a connection with the terms used in later reference books.