Board Thread:Wiki Discussions and Support/@comment-25977287-20150106122617/@comment-4516570-20150106155313

It's pretty unlcear, since this particular instance is viewed from much slower characters' perspective. That makes it very possible that it was Shunshin (as I recall, Rin mentions this) because the difference between 'holy-oh-damn-that's-fast' and 'instant movement' becomes insignificant, as opposed to when Minato faced A, and any less than instant movement wouldn't have sufficed.

However - In this instance, it is also very possible that he is using Flying Thunder God since he had already given Kakashi the kunai at that point.

It is said that FTG does not include smoke or sound, but we have since seen that that is arbitrary and smoke can indeed occur.

The thing I usually go by to determine the difference is momentum; when Naruto had just learned his Nine Tails Chakra Mode and slammed Kisame into the wall, there was a whole big debate about whether or not he used FTG or pure speed, to which the most compelling argument towards speed was momentum. In the scene you present, Minato seems to just sort of 'appear' - There is no indication of him departing his initial position, traveling, and then arriving at his destination (i.e. movement lines, weak argument, I know) - There is no momentum.

There is no definitive answer though, it's a situation where both seem equally viable.