For this question to be asked in a Japanese classroom and then saying that Germany started WW2 is a bit weird. As the war in Europe only really started on 01-09-1939, but the Sino-Japanese (aka more or less China vs Japan) started 07-07-1937). So if we count that conflict as being part of WW2 (which i certainly would become later) you could say that the Empire of Japan started WW2.
So it feels quite weird for a Japanese teacher to tell a German kid: Yes WW2 was started by your country...