I'm not sure that there was an conscious attempt to romanticize it by linking it to the Civil War. It's probably just the general obsession that America has over the Civil War that makes it such a lovely starting point for the story.

Since it was the first recorded fatality of a McCoy involving the Hatfields, it's easy in the mind to try and use that as a causal link to the feud that followed. But the parallels aren't there, as I mentioned, because the community was not at all divided over the war. Not that facts ever got in the way of a good legend.