Now if you put your grill on his porch and he continued to use it as if it were his own; yea I think he's ok.
Or to make it more accurate to this situation then if you trusted your grill to a friend, who put it on some dude's porch then who do you hold responsible for that? You blame this guy for using a grill that was put on his porch?
Nope. Nope. Nope. It's a very good analogy. The money was there where he could take it. He knew it was not his. He deliberately took it.
In the case of my grill, someone saw that it was available and deliberately took it. Whoever took it didn't gamble it away - they probably sold it. Either way, they took something that they knew was not theirs.
The bank left the money where it could be taken, just like I left my grill where someone could just wheel it off. They bank may have made a mistake, but it was not their fault that a criminal decided to take advantage of the situation and steal the money.