Without much information from the original post, here are my views:
I agree that registrar wants to show the client management that they look into every finer details of the system.
But one cannot argue that this not a valid question under 7.6.
Let me project scenario where this question can be vital:
The Software vendor designed the software to be an off-line analysis tool.
whereas the user has connected the software to the manufacturing equipment through a commercially purchased interface to perform Real-time SPC for "Special Process".
In this case:
The Software may not support the heavy load of data flowing in from the Manufacturing equipment. (The software was never intended. If they had, they would have performed Load and Stress testing during the Test phase).
The software may loose data during rapid transfer
The software may receive corrupt data, hang up during operation,etc.
Interface testing is a Software requirement if original Software requirement called for.
Another scenario:
If you are using a reputed Mitutoyo, Trimos, Tesa, etc... tools that come with standard catalogue interface and Catalogue software, then Manufacturers Certificate of Compliance would do. The rate of measurement is also slow and you can demonstrate that the value measured is the input value for the stat functions similar to what Mike and Hershal mentioned.
Regards,
Govind.