So I would be inclined to think it was a nickname.
Back then, though there were exceptions, there was not as muc importance placed on creativity as there is today. IN general, while there was theoretically a large pool of names to choose from, in actual practice, many more people were named in what we'd now call the top 100 than are named from that pool today. Loads more Johns, Williams,
Georges, Marys,
Annas and Sarahs.
(Also, men who worked the frontier were by nature transient, and often on the shady side, trying to escape their pasts or make fresh starts. They wouldn't necessarily keep the same name when they moved onto a different ranch) And often men were known by the names of towns they'd distinguished themselves in, so you'd have
Cheyenne,
Abilene, Reno, that kind of thing.