I think that the choice of the pirate book is rooted in a desire to clear Schatz's mind of being under the weather. Pyle's Book of Pirates is a book intended to capture the imagination of particularly young readers.  The vision of sun and bright colors accompanying the work with Pyle's illustrative abilities is a natural choice for a child who is sick with a fever.  The feelings of cold and discomfort can be easily channeled into far off places, helping the mental fatigue and anguish from being ill to dissipate.  The fact that the father reads the book to Schatz and then reads some of it to himself is a form of escapism from the challenging conditions of getting well. The romantic vision of pirates that Pyle evoked out in his book could be an attempt to capture the imagination of a sick child.  In the hopes of getting the child to become well, enlisting his imagination to think of far off places with exotic individuals such as pirates could have served as motivation for the father to choose this particular book to read. I think that it is a natural choice of text for a father to read to his son in the hopes that he can provide some comfort to a sick child in order to get well soon.