If they'd called the bank the next day, the bank would certainly have reversed the transaction. If they'd made a fat finger error on the blockchain, there would be no one to call. It's entirely possible for a fat finger error to send $10M to a nonexistant blockchain address, so you can't even work it out with your counterparty; the money has been destroyed (assuming the network is secure in the first place).
If you think this is how money should work, or how a certain settlement layer should work with reversals implemented in a higher layer, fine. But this incident is certainly not a counterexample to this argument.
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If they'd called the bank the next day, the bank would certainly have reversed the transaction. If they'd made a fat finger error on the blockchain, there would be no one to call. It's entirely possible for a fat finger error to send $10M to a nonexistant blockchain address, so you can't even work it out with your counterparty; the money has been destroyed (assuming the network is secure in the first place).
If you think this is how money should work, or how a certain settlement layer should work with reversals implemented in a higher layer, fine. But this incident is certainly not a counterexample to this argument.