In explaining application of unrestricted wording, the book’s note raises the Hanafi methodological issue of adding a restriction on the basis of a solitary report or analogy.
A khabar al-wahid is a transmitted report that does not reach the level of tawatur. Qiyas extends a ruling from an established case to a new one through a shared effective cause.
The takeaway is that adding a legal condition requires attention not only to whether some evidence is cited but also to its methodological authority. This short passage does not resolve every related juristic disagreement.