If you were unaware how or if a piece of computer equipment was modified, and said equipment had accessed very sensitive information, and you were charged with ensuring it was all destroyed how would you do it? I would think the simplest and, relatively, full proof approach would be to recursively destroy every piece of equipment and anything that it had touched.
Probably no more rhyme or reason behind it other then that. Of course given that logic they could have simply burned the whole building to the ground so we should give them credit for showing some restraint ;)