Tracon Coordinator reported a Flight Check aircraft received a low altitude alert while descending to 3;000' when the intended assigned altitude was 8;000'.

Narrative

While working the Coordinator position; I was coordinating a local IFR clearance and a radar hand-off with ZZZ1 Approach. I do not recall hearing the initial contact with Aircraft X; as I was off-line from monitoring the H position on voice lines. The last radar scan I completed with the aircraft was when it was descending from approx 9;600 to what I believed was SOP; 8;000. After completing my coordination functions; I scanned the radar again and observed the Low Altitude Alert activated on the aircraft. I immediately advised the Controller of my observation and she took corrective action. The aircraft climbed without further incident. The pilots are aware of the terrain in the vicinity as depicted on the approach plates and could have questioned the lower altitude. Controller advised pilot of an assigned altitude of 8;000; he advised he read back 3;000. I was not able to confirm or deny without listening to audio tapes. Therefore; it is difficult to make a plausible explanation for this section.