Kirk here with some statistics on “foreign workers” in Kumamoto. The category of “foreign worker” includes people like me (I’m a worker in the educational sector) but would not include foreign students at my university. I’m not completely sure but I think that the foreign children (those without Japanese citizenship, even if born here) may account for rest of the gap between the total foreign population (now nearly 20,000) and the approximately 15,000 figure in the report.
I’ll provide a citation in a comment and some explanatory notes for each graph (if you click on an individual graph, you should be able to see my notes).