Thank you very much for showing this excellent and unusual gun @Feltwad.
We should consider, that the American Longrifle has genes from the Jaeger-Rifle and the Trade Gun, and style and decoration/carvings have been influenced by european guns. European fashion came rather fast to the remote areas on the frontier. Most of the guns in the colonies and the young US have been imported from Europe. So the presence of european guns might have been sufficient to influence the style of guns made by american gun makers. Furthermore they used locks and parts imported from Europe.
It is the same thing with powder horns and powder flasks. A lot of horns and flasks have been made in Europe for export, and european metal powder flasks have been rather popular in the US, and have been used also in combination with longrifles. Later US-companies copied some design of european flasks.
IMHO there has been an exchance of technic and design, and it is rather interesting for me, to see european guns (that have been also used in de US) in a forum that has a focus on the American Longrifle.