SQF8's Glossary definitions for GMP and PRP are respectively -
(1) GMP - The combination of management and manufacturing practices designed to ensure food products are consistently produced to meet relevant legislative and customer specifications.
(2) PRP - A procedural measure that when implemented reduces the likelihood of a food safety hazard or a food quality threat occurring, but one that may not be directly related to activities taking place during production.
(Strangely vague definition and with no specific mention of GMP)
One can find a substantial range of PRP definitions elsewhere, often longer than those of SQF, eg NACMCF -
Prerequisite Programs: Procedures, including Good Manufacturing Practices, that address operational conditions providing the foundation for the HACCP system
This thread has some parallels with a previous one which also originated from "confusions" -
https://www.ifsqn.co...tc/#entry157452
I speculate that the auditor comment referred to in OP reflected some auditor's equally increasing confusion (desperation?). 