Its making the rounds again now because the guy who found it finally got someone to translate the full manuscript and announced this last week, at least in our local Phily papers which ran short blurbs. Since then it seems to have been picked up by national and international sources that maybe never saw the original report, or you know, slow news day and CATS! Local articles made note of this being an old find, but just with more information now.
Turns out they are not rocket powered cats, but rather the entire thing is about how one might burn down a besieged city by taking advantage of the many feral animal that cross over the castle walls by night and day. Cats and birds mainly. The flames aren't rockets but long burning incendiarybombs.