Interesting testimony, Neil.
A YouTube video confirms -
It seems that GIs remembered this song on Radio Tokyo during the war. Like "Shi-na-no-yo-y(*r)u, Shi-na-no-yo-y(*r)u-yo", this was sung proudly by GIs stationed in Japan in the postwar.
During the Pacific War, this song was used for overseas propaganda by Radio Tokyo. US soldiers who listened to it called this song "China Night (Shina-no-yoru)" and sang it. After the war ended, they competed for records in Japan.
View: https://www.youtube.com/watch?v=u6z1h82C7ms