The competitors from the kumdo dojangs are Americans, are they not? The American anthem is for them, like it is for every other American. They're not visiting from another country, like the Canadians do. It's common practice to play both anthems at hockey games where there are Canadian and American teams. The Japanese flag is because it's a Japanese martial art. Do you argue the Koreans should get their flag too just because they're really good at it?