The fact that he is sued, then there's a ground that he committed a crime.
It was mistakenly sent to his account but he did not tell the bank about that, he himself is aware that the money is not his, so he has to report it to the bank just to be safe. What if for example the amount of money wrongfully sent to his account is link to illegal transactions, and he spent the money, so he might be charge to be connected with the drug transactions, so the morale of the news here is we should be responsible, we should not be greedy.
He was guilty for using money that wasn't his in the first place, I mean his guilty consciousness didn't tell him that you can't just have money out of no where.
This same scenario ones happen to a friend but this was not a palliative, it was mistakenly deposited into his account and he wanted to make a smart move by transferring the amount into his second account so that the banks wouldn't notice since he didn't expect money from anyone and he never sent account details to any person, so literally he wasn't expecting money in the account. He was shocked when the bank visited his family house with a police after series of emails to return the money to the bank which he refused and negative was written on his account meaning he was owning the bank. The money was later return and case was closed.
The man should have question the source of the money but I think was waiting for an opportunity to gamble which the fund acted as catalyst for him.