At first I was like:"How it that possible?!" but after waching the video, it makes sense that you died that way. In fact, when you are to the left end (or right end) of the conveyer, a spawning pie can go under your hammer and kill you. It's like if the hit detection is different when there's a spawning pie, so your hammer doesn't always have the time to hit it before it goes under your hammer and kill you. When I run toward a pie at the same place you did, it also happened to me that I died. But when you smash the pie in any other place on the conveyer, you won't die.
Hope it makes sense!