Which interpretation best fits “الْقَصْرُ بِالْعَطْفِ” in context?

Qasr by Coordination, Negation–Exception, and Innamā

• Lākin and corrective contrast — Zayd is not a writer, but a poet.
• Four devices of restriction — Restriction through coordination.
• Restricting the agent — Only Zayd came.
• Restrictive force of innamā — The believers are but brothers.