I think KKK/TBH didn't show great sportsmanship, but on the other hand they didn't do any very bad thing either. 

Doesn't matter that KKK/TBH weren't the aggrieved parties... they should have politely asked the ref to give the point to the japanese because they clearly saw what happened and i'd bet my life that they won't be given a card for asking... that would have been the right and decent thing to do.
For example:
"the French Open a few years ago, when two Spaniards who were also friends faced each other in the finals. Neither had ever won a Grand Slam tournament. Carlos Moya won the first set and had broken Alex Corretja's serve once in the second. He was serving, however, and was behind in that game. Moya hit a powerful serve that was called out. If the call stood, it would have given Corretja the game and evened up the score. But Corretja overruled the linesman, giving the crucial point to Moya. The game went back to deuce and Moya eventually won. Steve was so impressed that he has rooted for Corretja whenever he plays.
In another case, Andre Agassi was playing in a major tournament and was scheduled to meet Pete Sampras in the final. Sampras, however, came down with food poisoning and could not get himself together before the time of the match. Agassi was told he had won by default. Instead, he suggested waiting to see if Sampras would feel good enough to play a little later. He did, they played the match, and Sampras won. This experience confirmed Steve's belief that both are great sportsmen and exemplary champions."
from: http://www.ethics.org/resources/articles-organizational-ethics.asp?aid=826