The Wikipedia article you linked to says that work was not peer-reviewed and four academic reviews were published criticising it (with only one positive review which still said it had shortcomings). You can choose to believe that Chernobyl killed just shy of 1 million people but that's at odds with all peer-reviewed research on the topic (which projects it will reach the mid-to-low thousands in total, with the current death toll in the hundreds at most).