In what way is Owen Barfield's 1925 fairy tale The Silver Trumpet a precursor to other fantasy books by the Inklings?

The 1st fantasy book published by the Inklings

Once upon a time there were two little Princesses whose names were Violetta and Gambetta; and they lived in Mountainy Castle. They were twins, and they were so like each other that when Violetta came in from a walk with her feet wet, Gambetta was sometimes told to go and change her stockings…

So goes Owen Barfield’s fairy tale The Silver Trumpet, written…