I think not too. I have been shooting black powder firearms, both percussion and flintlock, for well over 50 years and I never heard of iron pellets being used in them. Maybe the "journalist" who thought it was a musket type weapon, thought lead balls were iron pellets.
The little plastic bag seems to contain lead balls, and a black power measuring scoop. Add black power and small pistol percussion caps, which he may have also had, and you could shoot that thing.
Users put anything into a blunderbuss. With wadding that surrounds the ball, steel could certainly be shot from a black powder weapon.