Afraid not, you only retain the right to reject the car if there is something fundamentally wrong with it. If your friend was told that it had folding mirrors, then he might be able to reject it but even that would be a bit of a stretch. You don't say which trim or spec his old car or new car was, but he may have spec'd folding mirrors (or picked a trim level with them as standard), but that doesn't mean they're standard on the model he bought.