The 340 cipher

Just saw the film and I'm wondering if I misunderstood something. I was always under the impression that the 340 cipher has never been decrypted in real life. But the film showed one of Graysmith's kids asking him about what looks like the 340 cipher. The next scene of a televised interview then seems to imply that Graysmith had decrypted it. Was the film just taking liberties there in implying that it's been decrypted or did I misunderstand the scene?