Indeed. It would hardly be more clear if a little flag popped out reading "I am still dangerous." I wonder what sort of misunderstanding causes a person to think this is reasonable.

It struck me as ridiculous when I heard the story, but I can somewhat see how it happens -- first, civil-war era means that it is /old/, which makes it seem less dangerous unless you know about the age->instability relationship with explosives; second, it looks like an inert ball of iron, so there is nothing that really screams 'hazardous' to an uneducated viewer.

I can understand thinking that it's inert and safe initially, but the fact that it warms up when shaking it conclusively disproves that idea.