The place he was now in was likely a public facility used to temporarily store bodies; the voice outside the coffin probably belonged to the caretaker of the facility.
The caretaker seemed experienced. He referred to the disturbances coming from the coffin as the "Restless One" phenomenon, and he conversed clearly and calmly, showing no sign of panic during the process.
The body he currently possessed seemed to be that of a miner who had died from a fall from a height, the body suffering severe organic damage.
While conversing with the voice outside, Duncan was silently gathering this useful intelligence, all the while confirming his thoughts that this body was hardly fit for use.