The author does use an observation about the book Horatio wants, but he uses it to draw a specific conclusion about that same book, not a general conclusion about similar books.

The author doesn't claim that the library system is deficient or that it failed to control the book. He simply argues that, since the book is missing and other explanations for its absence have been ruled out, it must have been misplaced or stolen.

The author never rebuts any conclusion about the book; he draws a conclusion by eliminating alternative explanations. He also doesn’t apply any generalizations about most books to the particular book that Horatio wants.

The author never rejects a generalization, nor does he show that a generalization fails to hold in the particular instance of the missing book. Instead, he supports a particular conclusion about the book.

The author supports his conclusion by ruling out other possible explanations of the book's absence. Since no one is using it, it isn't checked out, waiting to be shelved, or part of a display, he concludes that it must have been misplaced or stolen.