This definitely falls into the category of someone having too much time on his hands.
The neat part about this is the amount of work that went into it. The hacker who made the xylophone had trouble finding books at first. Most didn’t have a good sound, so he soaked the books in a glue solution and then a sugar water solution. I t didn’t help any. Then he noticed that O’Reilly printed books on a different quality of paper, and he was able to use them as-is.
There’s a fair amount of detail on his website (in Japanese), but what made it through Google Translate was mostly gibberish.