But a proof/formal methods can't actually prevent you from being wrong because you can be wrong at any meta level.
Oh, this is a definition of "correct", it's not me correcting the OP.
I remember that in my computability theory class, defining the right proof was by far the most difficult task. And this was in very small, closed systems.
That is of course correct. However, it was my impression that the contract mentioned in the OP was completely on the blockchain, and therefore completely deterministic (no oracles or whatever.) Hence I figured it could've been proved with absolute rigor, in which case it should've been possible to formally prove the correctness. I'll be honest, I didn't look through the contract in detail now, so I might be wrong.
It doesn't change the fact that the crypto system lives in a human world were law, politics and attacks can coerce you to do a lot of things and the formality of the system is just irrelevant.