فَنَقُولُ هُوَ مِنَ الِاسْتِفْهَامِ وَلَيْسَ شَيْئًا آخَرَ بِرَأْسِهِ
Thus it is treated as an interrogative use, not an entirely separate category.
The hamzah in alā tanzilu binā enters a negative verb. The speaker is not merely seeking information about the guest’s intention; the real purpose is to invite the guest to stay.
This supports treating ʿarḍ as a transferred use of the interrogative rather than an independent basic grammatical type. Form, intended speech act and consequent clause must be distinguished.