What are the chances of not dropping said knife if one is suddenly yanked overboard and pulled under water?
Why would he have his knife in his hand before he was already being dragged overboard, it sounds like he was totally surprised.
Why would you want to argue against the everyday tool that he should have had on him and that would probably have saved his life, anyway?
I guessing you missed the 'sheath' part where it stays until you use it. You don't carry it around in your hand or between your teeth. It is a tool, don't be afraid.