It is the French St. Etienne proof (Wirnsberger, P. 132), but that source says it dates only from 1869, which I would think a bit late for that kind of pistol, unless it was made for the colonial trade. Anyway, no doubt as to its country of origin. It has little collector interest or value, at least in the U.S. Retail might be $100+ as a novelty.
Civil War? Unless Wirnsberger is wrong, no. It is, however the kind of pistol that was sometimes carried by soldiers for close up defense. I suspect the person who put the exhibit together didn't bother to check further.
Jim