I have completely remodeled this quiz, I used a manual distance calculator to find this distances so they may not be perfect. If you think I have made any mistakes, tell me and i will fix it if I can. I have tried not to use any disputed territories in this quiz.
It depends who you decide the Kuril Islands belong to! Both Russia and Japan say it's theirs. The closest undisputed distance, which is between Hokkaido and Sakhalin Island, is 43 km.
Your source is just plain incorrect. Russia is easily the closest nation to Japan, and There is no way on earth Brunei is closer than Malaysia, which is not on this list.
Hi Tyson, Cool quiz idea! I think maybe these distances have been calculated center-of-country to center-of country, which would explain why Russia and China are listed as being so far away, and Brunei appears as closer than Malaysia. That's one approach; I've posted a quiz here that uses the shortest distance between the countries. I'm not saying my approach is more or less "correct" than yours, it's just another way to work this quiz.