I agree it's not the first choice for a dirty bomb, but if you actually have access to a truckload of it, I can presume it's "good enough" rather than passing on it in the hopes of finding something better.
A truckload isn't all that much. I doubt the truck in the article was carrying more than a couple grams of the actual material. The lab grade sources we use (that are considered safe to handle as long as you don't eat them) are on the order of micrograms.
