If you're not close to the actual source of the radiation, that's mostly true. The methods ER is talking about were designed to deal with bomb fallout, which is essentially dust and particles whose elements have been converted to radioactive isotopes by the massive neutron flux of an atomic explosion. It is essential in dealing with fallout to prevent this stuff from getting on your skin or more importantly, into your body. Even alpha emitters can be deadly if they are inside you. Some elemental isotopes like Iodine-131 are dangerous because they accumulate in a specific part of the body, increasing radiation damage at that point.

Isotopes are also created in nuclear reactors by fission neutrons, which is why leakage from the core is a hazard. And of course, the fuel particles themselves are radioactive.

One radioactive isotope can cause radiation damage to living cells, but it can't make another substance radioactive. You could bury a can of beans in fallout for a week, but if you safely recovered it somehow and thoroughly cleaned it off, the beans would be safe to eat.