نِعْمَ رَجُلًا زَيْدٌ
How excellent a man Zayd is!
In this formula of praise, a pronominal element connected with the agent of niʿma is understood alongside the specification «رجلًا». The rhetorical setting is commendation: the listener first encounters a strongly approving appraisal, and the specification then clarifies its class.
The source treats the construction as a possible instance of pronoun replacing an overt noun. The issue is not the bare presence of a pronoun but its reference, its grammatical explanation and the effect of delayed specification.