The article is talking about plutonium 238, which is used for radioisotope thermal generators -- its radioactive decay is such that a big enough lump of it glows red hot all the time. We've never had much of a capacity to produce the stuff, and bought a lot of what we used from the Russians.
Pu 238 is a fascinating isotope.
Fairly hard to produce but there is nothing like it.
88 year half-life so it sticks around long enough to get work done.
No serious gamma emissions to worry about killing everyone around it.
If you try and build a bomb out of it, it melts long before you get to critical mass.
I know the difference and stand by my comment.