The textbook considers an objection: why does reversing a sentence with a locative predicate sometimes yield a false statement?
The answer is that the predicate is not merely the name of a place; it is being located in that place. Reversing the bare place-name changes the original predicate and thus fails to produce a valid converse.
From “Some people are in the garden,” we cannot derive “Some gardens are people.” The valid converse is “Some individuals in the garden are people.” Word-order reversal is not the same as conversion of the whole predicate.