The following is not accurate -

"Uranium reactors produce a mixture of depleted uranium and plutonium as a by-product of fission. "

Depleted Uranium, naturally occurring Uranium-238 is not produced in reactors. Uranium fuel pellets contain enriched uranium which contains a higher percentage of Uranium-235 than natural uranium and a smaller (but still present) percentage of naturally occurring Uranium-238 (aka Depleted Uranium). Plutonium-239 is created when Uranium-238 captures a neutron from the fission process.

In what sense is that quote not accurate?

Although the plutonium is not a fission product, it is indeed a by-product of the fission process. And after the fuel has been used, much of what's left is either the original U238 (which even after enrichment in fact usually far exceeds the U235 in the fuel) or the P239 to which some of it was converted by neutron capture. Although the U238 was there from the outset and so not "produced" by the reaction, the new *mixture* of U238 and P239 (and various fission products) is indeed produced from the old mixture of U238 and U235.