Naruto chopped her arm off with his own hand and the kunai you're calling back to was enhanced with Rikudo chakra. You saw the punch on Toneri yourself, which...well, calling it a byproduct of the local gravity is not really a strong argument in this case.He
ripped her arm off, kakashi stabbed her, kaguyas durability is against blunt force, now post the scan where. Naruto punches her with his so called unparalleled strength
The arm has life as its connected to Naruto. outside of that...not so much.The arm is having life as it moves , life is so much more than you see