Mind you, I'm not endorsing that theory, just floating the possibility, or thinking "aloud" as it were. It seems to me, if it were some type of intentional terror some group would have claimed responsibility, or there would have been a coordinated effort so it was obvious (i.e., 9/11 or 7/7).
But what better way to be able to keep up with little acts of terrorism than to not take credit for it and let people keep thinking that it was an accident?