Some suspect suicide or he was an agent for another power, but nothing has been proved. What is known is that he knew better than to yank the control rod out and he did it anyway. WHY???
There were rumors he was cheating with one of the other operators wives.
One theory is, the rods had a habit of getting stuck. He may have been pulling on it with considerable force when it suddenly became un-stuck. Overtravel. Boom!