Originally posted by Bentley
Well, personally I think Naruto pulled the feat by sheer speed, BUT since Kishi loves to give random upgrades to his characters, it's possible that he just learned by tapping into his Mom's/Dad's chakra or something. Which would be absolutely lame, but Kishi has done the "plot device/chakra lend/jutsu teaching" stuff before.
Can it really be called a random powerup if Naruto has done it before?
Only difference this time is Naruto wasn't attacking anyone and is more experienced with using his chakra in this mode.