If «وَهَلْ نُجَازِي إِلَّا الْكَفُورَ» is understood as referring to the particular severe recompense just mentioned, its sense is: Do We inflict that particular kind of punishment on anyone other than the persistently ungrateful?
On this reading the second clause needs the preceding report to determine the scope of “recompense.” It is strongly tied to its setting rather than operating as an unrestricted maxim about every kind of reward and punishment. This matters when classifying whether the appendix is cast in the manner of a proverb.