Maybe it partially melts the existing paint so that it then spread around over the scratch for the solvent to then evaporate and the paint harden again?
I bet it was in the Tat Zone. Y'know. The back end of the colour supplement where Thora Hird advertises stair lifts or some such. Actually there are usually shoe ads there, shall I tell PU?
Saw a TV advert for it today. Looks like an American invention. It shows the pen moving along several different scratches which appear to miraculously disappear.
IMO a bit of camera trickery. Watch it if you can. You'll see what I mean.