There is a simple explanation.....
ISO/IEC 17025 is the accreditation for laboratories.....it includes requirements that do not exist in ISO 9001, specifically technical requirements. 17025 assessments require technical assessors trained and experienced in the specific disciplines included in the scope of the laboratory. Additionally, this is an accreditation, not a registration.
ISO 9001 does not address technical requirements at nearly the same level, and your 9K auditor may have an entirely different background than what the organization does. However, 9K is good for manufacturing but gives an incomplete picture of the capabilities of a laboratory.
You may also find that your laboratory's customers CANNOT accept ISO 9001 without ISO/IEC 17025 also.
Hope this helps.