You’re making this sound like some Ocean’s 11-level heist, and then discounting the premise you’ve created as being absurd.

It doesn’t have to be that complicated. Perhaps he saw that the bank was in trouble and made a decision to sell shares when the company was at a 52 week low. His calculus could just be: “with the information I possess, this price could go a lot lower.” He may not have foreseen an insolvency event, or perhaps he knew it was a risk and he sought to hedge it. Or maybe he just sold it randomly at a low price … because.