وَ«غَيْرُ» كَـ«إِلَّا» فِي إِفَادَةِ الْقَصْرَيْنِ
Ghayr, like illā, can express both major directions of restriction.
When ghayr excludes alternatives, context determines whether a predicate is confined to a subject or a subject is confined to a predicate. Its presence does not force one fixed direction of qasr.
مَا زَيْدٌ غَيْرُ شَاعِرٍ
Zayd is nothing other than a poet, in the context under discussion.
That restrictive reading must be distinguished from simply using ghayr as a non-restrictive descriptive contrast in another construction.