When you get into a vault, you don’t have access to the length of cable you might think. Argues against it being guys out for copper.
I’ve seen guys put a lot of work into getting a very small amount of copper. I’ve also see them be total idiots and cut the copper out and leave it taking cheaper metals. Stupid thieves seems a lot more plausible that terrorist plot to me. Terrorists are out for blood, big showy displays of parts, not minor inconveniences.