Update on this developing story.
Yesterday, the Russian Consulate General in Sapporo tweeted that they had not been in contact with the man who crossed over from Kunashir. However, they also tweeted that he had not swam, but instead used a rubber boat to cover the 25km distance.
The press has also learned that the man was in possession of Japanese yen, which he used to buy clothing and beverages in the Town of Shibetsu after landing.