This image from weather.jp gives us a clearer idea of how big yesterday’s earthquake was:
https://weathernews.jp/s/topics/201905/100848quake/
It says the quake was M 6.3 which explains why it felt so strong even though the epicenter was fairly far away. M 6.3 is a big release of energy. Perhaps the distance explains why it seemed to sway in Kumamoto instead of lurch.
The Japan Meteorology Agency (JMA) has pretty much the same information (in English) on the following page:
https://www.jma.go.jp/en/quake/6/20190509235307493-10084852.html
– Kirk