I think this may be an example of trying to shoot yourself in the foot by only doing the bare minimum required to meet the requirements of the standard.
4.2.1.d requires "documents, including records, determined by the organization to be necessary to ensure the effective planning, operation and control of its processes."
Such records will surely include preventive maintenance records.
If a machine needs regular PM and you don't record the date it was done, how do you know when it's next due?
If software needs patches or updates (which it always does) and you don't record them, how do you know that current patch status on all relevant machines is as it should be?
If there are returns from the field and root cause analysis indicates a manufacturing fault, and you don't have the relevant preventive maintenance records, how do you eliminate lack of PM as a possible root cause?
No, they're not mandatory. But why not ask which PM records would be helpful?
Why not engage the auditor in a conversation of mutual respect and ask what he or she is looking for? Sure, they're not supposed to give advice. (Did the auditor actually say, "keep PM records," or just ask if you had considered them? If the latter, it's not advice, it's a question that's designed to help you reflect.)
But suppose the auditor has been looking at nonconforming product and its data, and wondered about preventive maintenance of critical machines, and couldn't find any? Why wait until his or her next visit to discover that you haven't met 4.2.1.d with regard to ineffective root cause analysis of manufacturing faults due to lack of preventive maintenance records?
Hope this helps
Pat