This theory has absolutely no evidence and is just a guess but Minato's and Tobiramas techs were incredibly similar. They both knew s/t ninjutsu apparently.
They were both able to sense enemy shinobi by putting one finger on the ground.
Tobirama was also a waterstyle user . Minato's element isn't revealed but it is widely theorized he had suiton.
Or perhaps he read the damn scroll of seals and seen it there. I mean it had tons of forbidden techs. Edo tensai could have been one too.