2003 Honda Accord Bent Piston

Recently the car would not start - had to have it towed to Honda Dealer. They said there was diesel fuel in the gas tank and would have to empty and flush the lines and see if that would fix the problem. It did not and now they tell me there is a bent piston and the whole engine will have to be replaced! How would they know that the piston is bent? The car would crank, but just would not start. As far as the diesel fuel in tank, I can not imagine how this could have happened due to the nozzle not even fitting into the gas fill tube. What is your opinion?