The discussion on printed page 168 uses «هَوَايَ» as an illustration of economical annexation. Adding the first-person pronoun to «هَوًى» can express a relation that might require a longer relative construction if spelled out fully.
هَوَايَ
My desire or the object of my affection, as context may require.
An annexed expression does not automatically settle every figurative or idiomatic interpretation. The point here is that a possessive-pronominal relation conveys the intended connection succinctly. Both the syntax and the speaker's purpose must be taken into account.