He may be referring to what most of us in the USA would call mineral spirits, paint thinner, PD-680, or white naphtha. It has a higher flash point than gasoline and won't affect most plastics. Commercial CLP sold for gun use is very similar to low viscosity synthetic motor oil. CLP is really all you will ever need for gun cleaning and lubrication. Naphtha is a very old generic term that can be applied to about any liquid hydrocarbon, somewhat archaic today.
I have no inside information, but it has been said that the plastic most used for handgun frames is a glass fiber-reinforced Nylon 66. If so, frames should be solvent proof as Nylon 66 is highly chemical resistent.