What has probably happened is the car was inspected at the bodyshop and the engineer wrote it off. The bodyshop probably a week or so later has been back in touch with the insurance company saying they can repair it for £XXXX amount. The insurance company probably said ok as the second figure the bodyshop quoted would have been less than them paying out the customer.

Tell him to leave the car and dont sign anything. Also get the original engineer to inspect it, also the AA or RAC.