It is reasonable to ask for clarification within the book, but what that clarification will read is something to the effect of:
Certain two-handed weapons are valid for blocking while held in one hand. This includes the Long Bow, the Short Bow, and the Staff. The Staff and Long Bow count as long weapons for the purposes of the Two Weapons fighting style skill. The Short Bow counts as a short weapon which means that Short Bow and Long Sword is a valid fighting style! Just remember the bow still requires two hands to fire; you'll have to put your sword away to use arrows.