Every time I have signed up for direct deposit I have seen clauses in the contract that I was required to report any mistakes and the company could recover the money from my bank account without giving me notice. I wonder if the recipients of the money had no contract with Citi, so they had no contractual requirement to return the money.
They had a contract. They were owed the money (to be paid by 2023) so it would be like you paying off your mortgage early and then going back to the bank and asking them to re-instate the loan and give you the money back.