I suspect that you are correct. I will point out, however, that rifling had been experimented with as early as the mid 15th century. Odds are good though that John Alden’s weapon was not a rifle.
When you are 50 cal, you don’t need to be rifled.
You just need to be close.
And brave!
Actually, the American Rifleman’s video “Ten Guns that Changed the World” didn’t mention this one.
But it did mention the Kentucky Flintlock.