I feel like that's less some anti-impersonation rule and more ChatGPT simply lacking creativity. I got similarly stonewalled when asking it about how much wood a woodchuck could chuck if a woodchuck could chuck wood, with responses along the lines of "that's a tongue twister, woodchucks don't actually chuck wood". Even after narrowing the possibilities (specifying balsa wood, specifying specific dimensions of the wooden projectiles, specifying woodchucks of average size/strength, even giving the woodchucks trebuchets), it still refused to give a straight answer, only saying that woodchucks wouldn't be able to chuck very much wood.