The plugin does not add a single-book-review.php to your theme, but it does check your theme for that file and, if it exists, will use that file instead of the formatting that is done automatically to single book reviews by the plugin. This is to allow theme developers to be able to customize their own template files rather than using the default formatting that the plugin uses.
If you are trying to create your own template file, I recommend taking a look at the inc/func.php for a bunch of functions you can use to pull in the book details which are used by the plugin itself. You might also want to take a look at the filters in views/public.php for ideas of how the plugin handles formatting that information automatically.
Otherwise, the plugin will take care of the single review layout on its own if there is no single template for the book-review post type.
