Or it's how the photons happened to hit his body. They might have hit in just the right way to not do cancer-causing DNA damage, or if that did happen, then tho

Or it's how the photons happened to hit his body. They might have hit in just the right way to not do cancer-causing DNA damage, or if that did happen, then those cells weren't influential or died or were terminated by the immune system by pure luck (he could have had the same level of "immunity" as those who happened to die because their system simply had an unlucky miss).