All he has done is polish the Plastic lens.
All plastic headlamps go like this! I did the same on my MX5 a few weeks ago. You simply start with some 1200 Grit Wet and Dry and the end with 2000 Grip W & D and the polish them back, I usually end using some G10 farecla. I've been trying to buy a Roadster over the last couple of weeks and everyone one I've looked at had this, it's a good bargaining tool if the owner doesn't know how to rectify it
yes mate this is pretty much what he did except he finishes it off with 2 coats of clear lacquer