Ahh I see - makes much more sense!

Basically, if the paint is very soft then removing the polish can be quite hard. Buffing the polishing compound away can leave cloth marring marks in itself. Soft paint IMO is the hardest to polish as it's so delicate and not forgiving at all!
Long, slow sets are required and then as little buffing as possible to prevent leaving marks.
Fair play to him for letting you know. Who was it out of interest?