The significance of the dance Harrison did with the ballerina was that Harrison was very graceful, almost too graceful considering his size. Him and the ballerina soared through the air, almost as if they were flying. This part of the story uses many adjectives that all mean 'soared' and this is different from the original style of the story because it is no longer about everyone being the same, but on the gracefulness of Harrison and the ballerina without their handicaps.
I hope this helps! I just read the story in English class a few days ago!