I would imagine that the request was for a
practice Cat3 approach.
This could be executed in (Cat1 or better) conditions, but no protection would be given.
If the weather on the day was good, then it was probably for crew training/practice.
However, I'm unsure of the legalities of taking it past the Cat1 DH to the B737 CATIIIa DH of 50', as the company's SOPs should state a minimum alt for autopilot disengagement on a CAT1 system.
LJ