Thanks for that; but I still fail to see exactly how and why death resulted. I notice you have a question mark at the end of your reply!
It's a simple as some unlikely falling block of cheese which landed on and killed the photographer. The joke is that everyone shouted cheese to warn the photographer about the impending hit but the photographer thought they were just saying cheese as they were being photographed.
You have to go with the scenario that the cheese was doing something likely to kill someone which everyone else could see but the photographer didn't. Unlikely, I know, but it is the premise of the joke