Your ART Assessor is not your mentor. ART Assessors have been appointed in order to ensure standards and accreditation consistency. They are invited by your mentor to watch you teach (hence an assessed lesson) and confirm that you have reached a good standard of teaching using ART techniques. They will hopefully recommend you a for accreditation.
They will want to talk to both you and your mentor, go through your teaching log book and confirm that the mentor has played an helpful and supportive role in your development as a teacher.
Usually someone is invited to become an ART Assessor after they’ve been using the ART Teaching Scheme effectively for a while, or they are a course Tutor. Where there isn’t an existing ART Assessor in your area, ART may appoint someone new at their discretion – usually an experienced teacher who is interested in maintaining good standards.