Correct. The relevant quote is subtly different however: “never actually got his hands on a radiation source, he tried to procure x-ray tubes from an undercover FBI agent posing as a supplier.” An X-Ray tube is itself a source, it doesn’t contain one.
One can only assume the intent was to bank up a heap of X-Ray tubes and power them up in parallel. X-Ray tubes are not exactly efficient, and you won’t build a laser this way. So at best (worst?) you would get a diffuse flux of X-Rays emanating from the truck, and if you were nearby the truck for any length of time you could get a dangerous dose.
However the power needed to supply (not to mention cool) the tubes is not insignificant, and the voltages and currents needed will turn you into a raisin. I would predict a swift and spectacular demise on the part of the conspirators.
X-Ray tubes used for inspecting welds and fabricated structures need to be pretty powerful, but their duty cycle need not be great. I would guess they were after these tubes, rather then diagnostic X-Ray machine tubes.