وَهِيَ إِمَّا بِمَعْنَى اللَّامِ، نَحْوُ: «غُلَامُ زَيْدٍ».
Translation: Semantic iḍāfah may carry the sense of lām, as in “Zayd’s servant.”
The relationship in غُلَامُ زَيْدٍ is explained by غُلَامٌ لِزَيْدٍ.
In the first, Zaydin is mudāf ilayh; in the second, li-Zaydin is an actual prepositional phrase.
Similar meaning does not make two different grammatical constructions identical.