- Japan acted sooner than most by closing schools, tightening their borders, informing their citizens and asking for their cooperation.
- Japan's culture is a big factor, people respect and obey their government in general, the use of masks is common place, practicing social distancing is already part of their culture, with no kissing, hugging or handshakes for the most part, the exception being their public transportation, which are well known for how packed they are near the Tokyo area.
- Japan has a good health care system https://www.who.int/whr/2010/en/
Lastly, let us assume that Japan isn't testing everyone they can as suggested by some, as a way to somehow keep the Olympics going.
- Japan has an older population, which is high risk group as we know.
- IF they are in-fact manipulating numbers as some suggested by not testing, than we would be seeing a spike in the death rate for the 60-80+ age groups. Now I can't provide a metric to prove or disprove this and the only thing we can do is wait and see, but I have doubts about the government ignoring their people in-favor of an event that likely won't happen this year or at least not the early half of the year.
EDIT: Lastly and this is a factor that none of us even suggested, is luck. Luck is important and impossible to control.