Trust me... I have a base coupe (for 5+ years) and those are the cloth seats that have been recovered with leather. Clearly done by a professional. No doubt about it! I can tell just by looking at the ***** and the shape of the seat (which is almost identical to SLK seats).

If that guy is the original owner and thinks it came from the factory like that then I am willing to bet the dealership did it and never told him. They probably prepared it for a potential buyer and the deal fell through. Then he came along and bought it.