That is a selective reading of the criminal code, literally Article 230 but ignoring Article 230-2. Japanese defamation law is not far removed from that of British and Commonwealth countries so in the interest of tamping down any "weird Japan" vibes that might develop I'd like to clarify that Japan is not incredibly strange in this area. There is a far greater schism between England and the United States than there is between England and Japan when it comes to defamation. But Japanese law in this area is quite conservative and many would consider it old-fashioned at best. Fortunately some of the really nasty stuff like lèse-majesté was abolished during allied occupation.
Article 230 sets up the baseline for criminal defamation: "A person who defames another by alleging facts in public shall, regardless of whether such facts are true or false, be punished...". It doesn't actually require any demonstration of loss, so in a way it's actually a bit worse! Article 230-2 states that the truthfulness is examined when the facts "relate to matters of public interest", and explicitly allows "matters concerning the criminal act of a person who has not been prosecuted". There are a few other things, e.g. truthfulness is tested in claims against the deceased and public officials/election candidates, and just insulting someone outright is punishable. Then there is the civil code, which is more about demonstrating lost reputation, getting an apology or compensation.
It is just my opinion but I would say match-fixing in Sumo is in the public interest, whereas (for example) the exact particulars of Ryuden's indiscretions would not. If any ever wonder why Japanese news in Japan can be so dry and informal it's partly due to laws like these.
