I do not believe that is true. If the clown fish were to get stung then it would also be paralyzed like any other fish, and then eaten. The reason that clowns and some damsels do not get stung is because of the slime coat the poses. When the anemone touches the clown it thinks it is touching itself.
Maybe Bang Guy will stop in and give a more detailed descriptions, but I believe what you were told id erroneous.