Process audit cover much more points, example (VDA6.3):
P5: supplier management + warehouses + supply inspection
P6: process release + maintenenace management + operators skils managements + process indiators + process output (also warehouses) + non conformity management (don't thing You cover tha by control plan) + control tools management (also included MSA) + ...
P7: customer satisfaction management and how customer service is providing (including aftermarket service, and elements how to be prepared for it)
process audit is not only describing this what is happend on production line - but also everything around: this is process