I don't believe it was originally a muzzleloader, either. Converted muzzlelaoders to breech loaders usually have much earlier, poorly designed breeches. The underlever and solid steel action speaks of primary manufacture.
Wiping sticks were incorporated on many ctg. guns in the States as well - to the order of the person having the gun made.
There were also some ctg. guns in the US made to resemble fit and finish (stock and furniture) of famous muzzleloaders of the frontier, mainly those of the Hawken Bros, but made by Sharps or Spencer.