I placed a picture of a two band Enfield sabre bayonet next to his bayonet and they look like a dead on match, hilt shape, gutta percha grip placement of rivets and the blade shape or what you can see of the blade, but it could like you said be another European made musket. Just my best guess. Remember this is just a picture of one man and one musket and this could have been taken anywhere in the south after about 1860, yet rare. Now on the other hand if the picture was of a company of men outfitted with the same musket and bayonet, now that would be strange and rare. Since he has no matching leather gear, this might mean a borrowed or photographer's prop weapon. Again just a thought.