To me that's good news. "Exaggerated" is a long way from denial and it's not unlikely that a lot of the teens in question thought of actual exaggerations when they answered. The extinction claims exist and they are vastly exaggerated. Climate change may kill more people than both world wars combined, but it's not going to get us anywhere near extinction. Even a nuclear war triggered by climate change wouldn't be able to move us from the "least concern" part of the endangered species list. The resulting famine might kill most humans, but you'd need a thousand times more nuclear warheads than in current inventories to wipe out everyone on the surface. And even then people in bunkers would survive.