Why did the kid...?

Well keep in mind that there are a variety of labs that _do indeed_ maintain stockpiles of various radioisotopes that they use to manufacture specialized isotopes used for industrial and medical applications.

If you have an old-style smoke detector, you have a very tiny quantity of Am241 or a similar alpha-emitter inside it. The smoke particles interrupt the alpha particles on their way to the detector - when the detector isn't getting a signal from the radioactive sample it knows there's smoke particles and therefore it sounds.

Also, photographic film/paper wiping brushes often have a small cage built directly next to the top of the bristles. As the alpha particles are emitted it induces a polarity in the brush bristles - making it FAR easier to brush off loose dust from the film prior to doing enlargements or making prints.

Just about every single cancer treatment center needs a variety of other radioisotopes for diagnostic and therapeutic reasons...

I'm not specifically positive if the Am241 used industrially/medically is produced by the DoE/NRC/etc or if it's just extracted by some trusted third party laboratory (like most industrial radioisotopes ARE) - but don't for a second assume there's _no_ plutonium outside of government labs - all sorts of college physics departments have samples of all sorts of materials you'd not expect them to have... just in smaller quantities than the "lab" from the film had.