Why is Holden 'so damn happy all of a sudden'

Holden feels 'so damn happy all of a sudden' at the end of chapter five for maybe a few reasons depending on how the reader personally views it. The first reason could be because when it begins to rain Phoebe takes the red hunting hat and puts it on Holden's head, when she does this Holden says that it 'damn near kills' him. This is his way how showing how Phoebe cheers him up and makes him feel better. Another reason why he is 'so damn happy all of a sudden' may be because it is nice to see his little sister being so care free and innocent. This may symbolise the innocence that Holden can't quite let go of and finds growing older hard to except. But Phoebe reaching for the gold ring on the carrousel and taking a big risk may show how she herself is growing up and gaining maturity. Maybe at this point he begins to to except the fact that Phoebe is growing up and maturing without turning into a 'phony'.