Therefore, the most likely theory is that that these flags represent the "Principal Allied and Associated Powers" as stated in the Treaty of Versailles.
This list consists of the following nations or Dominions: The United States of America, the British Empire, France, Italy, Japan, Belgium, Bolivia, Brazil, China, Cuba, Ecuador, Greece, Guatemala, Haiti, the Hedjaz, Honduras, Liberia, Nicaragua, Panama, Peru, Poland, Portugal, Romania, The Serb-Croat-Slovene state, Siam, Czech-Slovakia and Uruguay.
Given the "unflagging" interest what these varied flags mean, we hope that this mystery can be laid (somewhat) to rest...
Image caption: The United Kingdom flag, the White Ensign flag, the Red Ensign flag and the New Zealand flag, Hall of Memories, Auckland Museum