مَنْ جِبْرِيلُ؟
Who is Jibrīl?
مَلَكٌ
An angel.
The reply gives a kind or recognizable description rather than another proper name. It can still serve the question by making the individual identifiable to the listener.
Al-Sakkākī’s analysis faces an objection: a genus-like reply need not prove that the question was primarily about genus. The key analytical point is that a genus-like reply does not by itself eliminate the individuating function of man; the communicative context determines the required identification.