Wibbly Pig's state of mind

Wibbly Pig is lovely. After reading his exploits you always feel more happy than when you started. The pictures and the words are simple but captured in his face is contentedness even when stuff is going wrong for him.
There is something just right about books being written by Mick Inkpen. If there is anyone destined to be an author surely having such a surname helps. A brief surf through the internet does seem to confirm it is his real name, 'cause you do wonder.
I only discovered Wibbly Pig three years ago as before that I didn't really check out the children's section of the library.
So these days, on a fairly regular basis, we have Wibbly Pig visit our house in book form. The last one we had was entitled, "Wibbly Pig is Happy". In the story he mostly is happy - he suffers an unhappy incident but sees it through to happiness again.
However while it appears this is what is going on, it would seem a sadder story lurks underneath. The book maybe entitled "Wibbly Pig is Happy" but the scanner at the library printed it out on the receipt as, "Wibbly Pig is Upset."
This book has spent more time at the library than at our house so what has Wibbly Pig let slip to the librarians? Is he not as happy as he shows? Is he just wearing a happy face because that is what people expect? Is he internalising his issues of being anthropomorphized?
I guess we will just have to get the book out again in a few months and see what the library scanner lets slip.