Car Overheating with radiator cap off

The cap was off when I opened the hood. It had not blown off because there was no way it could of blown off and landed upside down next to the opening because there was not enough clearance with the hood closed for it to blow off. Also, if that would of happened, I am sure I would of noticed it happening.

It was the dealership owner that I requested payment from and who told me it couldn’t of gone that far and he didn’t believe that they did it. He told me to sue him if I wanted to.