forget that chapter for a moment and focus on this --
a many-to-many relationship is always implemented as two one-to-many relationships involving a common junction table
a one-to-many relationship does ~not~ involve a junction table, even if the "many" table is actually a junction table for a many-to-many relationship
if a one-to-many relationship actually did involve a junction table, then the data model in that chapter would be...
authors -- authorauthorbooks -- authorbooks -- bookauthorbooks -- books
like i said, using authors-authorbooks and books-authorbooks to illustrate one-to-many relationships is unfortunate and potentially misleading
... but not wrong