This is not a global study. It only involves OECD member countries. When you take all countries into consideration, the U.S. is 12th. Not that that's something to be proud of.
Secondly, the studies that "evidence" that high BMI "causes" various cancers and diseases do nothing of the sort. All they do is prove that certain diseases occur under the same conditions that cause high BMI. In a nutshell: obesity is a symptom of the same issue that causes the other conditions. More and more evidence is coming to light that it's actually high carbohydrate diets that are causing diabetes, increased rates of cancer, heart disease, AND obesity. Strike at the roots: don't blame one outcome of a junk diet for causing another outcome of a junk diet. Blame the diet!