For all we know, the only source of tobirama having s/t technique is minato.Minato personally did not see tobirama performing the technique.Minato might have learnt from jiraya who might have learnt from hiruzen who was tobi's student.Hiruzen would have seen tobi performing the ftg slash.We know how legends grow from a seed to tree and I think the same thing might have happened when the knowledge about jutsu was passed down from hiruzen to minato.Minato after developing s/t technique would have named his technique after tobi's except for slash because he doesnt use the sword.Ftg slash might be just a turbo boost technique with high acceleration.
This is my first theory.So if I am wrong correct me rather than pouncing on me.
This is my first theory.So if I am wrong correct me rather than pouncing on me.