Earlier quoted context omitted.
But he didn't take out a loan. The bank kept giving him money whenever he wanted to withdraw it. That is not a loan. A loan requires explicit agreement and a fixed amount.
He signed a contract when he opened up the bank account. That contract would have included clauses establishing liability for overdrafts, even if the bank account didn't include an overdraft facility.
Maybe the contract did not include such a clause? There's a reason why he got acquitted in the end.