Other studies have gotten the opposite results.
I think it depends on how the CBT is carried out, and for how long.
My own feeling on CBT is that it has to be adapted appropriately for a person with schizophrenia. I think if it is applied just as is, by a person who has little or no experience communicating with people with schizophrenia, I don't think it helps much. But when applied intelligently and sympathetically, I think it helps.
I don't think a brief period of CBT, all by itself helps much if the person goes right back to an environment full of stress, miscommunication and lack of understanding of the person's condition and experience. Perhaps some of the people around the person with schizophrenia, can learn to apply some of the principles of CBT in how they communicate with the person with schizophrenia, so it can become an ongoing improvement in communication.