You have to admit that it's a pretty HUGE coincidence. And I've never cut through a serpentine belt but I'd imagine it couldn't be that easy.. ? And if someone really was just being a jerk wouldn't it be easier and more costly to you, to just cut some ignition wires?
I dont know exactly who you are speaking of.. but I know that the "group" you are speaking of, and HIGHLY doubt they are capable of something like this.. besides being downright mean, it is quite illegal.