Are you sure this one was like that? I'd assume RTGs are a small enough market that they would be pretty much all be custom-made and tailored to the current requirements, and given this isn't a space probe and must be covertly transported by people on foot I would be surprised if they have the same amount of shielding/protection than the ones made for space.
Yes, this has happened many times with medical radioisotopes. People find them in a scrap yard, get amazed by the glowing blue powder, and leave a deadly trail of contamination until it's discovered what happened.
