Even if, for example, you find a loophole that allows you to make 100% guaranteed money, the deposits of the bank belong to the bank, they are not the personal funds of the CEO.
Like, putting money in treasuries is basically 100% safe. It's fine for the bank to put the money in treasuries and profit. It's highly illegal for the bank CEO to take 20 million from the bank, use it as personal funds, buy personal treasuries, and then put the money back.
The title makes it sound like the problem was that he was an idiot and fell for a scam. The true problem was that he misappropriated bank funds in the process of doing so... and if there's any one person you should expect to understand that line, it would be the CEO of a company (or I guess CFO if you have to pick one, but if you pick two it's CFO and CEO)