The phrase anta baʾin carries a notion of separation, but it does not identify the specific kind of separation in every setting. It may concern physical or relational distance, or—in a relevant legal context—termination of the marriage.
Sarih: the relevant intended meaning is manifest from the wording.
Kinayah: an additional indicator, intention, or surrounding circumstances help specify it.
The book's example concerns principles of divorce terminology, not a claim that every occurrence of this phrase necessarily constitutes divorce.