In that case, the customer was demanding repayment of lost money, alleging the bank's security was negligent, and the bank was basically asking the court to say "it's not our fault somebody got his username/password".
The deposit in question exceeded that which is guaranteed by FDIC.
And your summary was flat-out disingenuous; you presented it as the bank suing the customer, when in effect it appears to be the bank seeking a court declaration that the bank's own security measures were not at fault, as a response to the customer's claims against the bank.
In that case, the customer was demanding repayment of lost money, alleging the bank's security was negligent, and the bank was basically asking the court to say "it's not our fault somebody got his username/password".