The science has moved on from the time we called it junk DNA. It's definitely not junk and we now understand at least some of the reasons it exists.

The harms of radiation on humans are well understood. Of course, with high amounts of radiation we would likely evolve mechanisms to handle it, but that takes many generations. That fungus would have had many generations since the Chernobyl disaster happened, but we haven't. So, you can't really draw any conclusions about humans from this study.