And if this was a forgotten poster from his office or a lost book, no one would care. But it's ten thousand dollars. What do their feelings have to do with an obligation of that magnitude? Either they have to pay it or they don't. Who cares about whether he "deserves" it or not?
Also: you realize your intuition makes no legal sense, right? If you "agree that he should have been paid" then you are agreeing that Miso has a debt to jshwu. Debts don't disappear like that because of technicalities (or rather, not unless such technicalities are described in a contract that everyone seems to agree doesn't exist in this case).