Ummmm, Japanese people have rioted before. While riots have been very rare in recent decades, the decades after WWII had riots, including the rather legendary riots over the construction of Narita Airport (
https://en.m.wikipedia.org/wiki/Sanrizuka_Struggle).
There was even a riot in 1973 that broke out by train commuters who were enraged that they couldn’t get to work due to striking train workers back when the JR system was nationalized:
https://youtu.be/7QUfszx22w4