My original point was that Obito didn't know about FTG, since he stilled called it Shunshin during his attack on Konoha. Rin, even seeing it in person, didn't know about FTG, and called it Shunshin. Minato's underlings didn't know the workings of FTG, only that Minato was extremely fast/powerful and didn't question the order to throw the kunai into the enemy group.
The only people that knew it, for sure, in the interim period between the Gaiden and the attack, were Minato, Kushina, the 3 Kage guards (since they were taught it), and A. A only figured it out because he noticed that Minato would appear next to a kunai when he teleported.