Made in Belgium is not something you'd find on an original piece. Certainly we had imported guns in the New World. The Dutch, Spaniards, French and English brought in guns to trade with the Indians (and locals). Germanic or Swiss also brought their rifles or rifle making technology here too.
It's also possible (but not probable) that a worn barrel was replaced with a fresh Belgian barrel. It's not probable because it was not unknown for a gunsmith to ream out an tired, iron barrel and then re-rifle it to make it shoot accurately again.
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!