«فِي النَّسَبِ فَرْخِي وَفِي الْمُكْتَسَبِ فَخِّي»
By lineage he is my fledgling; as a means of gain he is my snare.
Farkhī / fakhkhī changes a fledgling or child into a snare through a compact phonetic shift. The paired frames fī al-nasab / fī al-muktasab divide lineage from the means of earning.
The son’s actual relationship to Abū Zayd is not itself a falsehood. The deception lies in exploiting that true relationship to stage a claim for gain. A reader should resist judging the entire story true or false on the strength of one accurate detail.
Capstone inference: one true detail can coexist with a dishonest scheme.