1.) There is zero evidence for FTG, just speculation.
There's evidence against it
perhaps. Naruto sprained his ankle due to momentum. Minato never showed momentum with FTG. Thus, Yamato (who over-reacts on everything) said Naruto was not at his father's level likely referred to linear speed, not FTG (albeit, he was not specific so I won't rule it out). Besides it's scientifically consistent that using a space-time technique must conserve your momentum, so the FTG user should arrive with the same momentum they departed with. Kishimoto isn't a physicist, so who knows if he knows this or cares. He already has people flying around shoot fireballs at each other, lol
2.) First, his father left him the Kyuubi along with his and Kushina's chakra with the eight trigrams seal on it, not the body flicker jutsu. Second, the body flicker technique is about as useful as much chakra you have and put into it, as it uses chakra to generate incredibly fast linear speed. The Raikage in raiton armor used it to dodge Ameratsu, Shisui was known and feared as Shisui of the body flicker, and Hanzou used it to get the hell out of town when Nagato unleashed Gedo Mazo.
Given that the Raikage using his raiton armor could dodge Ameratsu with the body flicker, what do you think Naruto could do with the Kyuubi's chakra? Given Naruto's speed and Kishimoto's lack of caring about illustrating handsigns like early in the manga, it's easily argued he could've made 1 hand-sign we didn't see. This is more likely than a ridiculously convenient FTG seal being right in front of Kisame.
3.) This is the easiest explanation, followed closely by 2, and that Naruto merely sprinted but was enhanced by the Kyuubi chakra like he was when he fought Neji in the Chuunin exams, Sasuke in the Valley of the end, and Orochimaru, etc.
Swift release doesn't even count, since it is only in the movies. All that counts here is the manga. Not to mention it makes little sense to me. How would Naruto have a KG that only works when he doesn't use his own chakra, which is due to DNA?
If you're convinced and no one can change your mind, then it's a waste of time to argue. Me, I just wanted to poke my head in one last time and try as well as clear up some things.
I'm certain it's either body flicker or sheer speed, and I have no doubts that it wasn't FTG (doesn't mean I'm necessarily right). Thus, this is likely my last post. Take care, and I hope you find the answers you were looking for. Cheers.