Very few athletes are actually overweight. The Olympics are on TV right now. How many of the competitors look overweight to you? Even in America only a tiny fraction of the population is really "buff"; they have a negligible impact on the overall percentage.
No the vast majority of Olympians really aren't classified as overweight. Check your data again. It's really only in a few sports which require short bursts of high power where you frequently see athletes muscular enough to technically fall into the "overweight" category.
