That makes sense, cosmic rays and such can do some pretty neat things; however, in carborane acid, the anion CHB11Cl11- is "[...] incredibly stable ... so it is non-corrosive like other strong acids."
Could that be why carborane acid is a such a strong acid? The extra proton attached to the carbon atom is so weakly bonded to the rest of the structure owing to near-complete ionization.
That makes a lot of sense, but it does not explain other carborane structures that are not acids. Could it be that the B—C bond is a "three-center two electron" system?