In all likelihood M. Scott Peck confused DID and DID-like DDNOS with schizophrenia. This is a very common mistake, made not only by laypeople but also by many trained mental health professionals.
I have read all of Peck's books. The Road Less Traveled, my favorite, was a great help to me in my first crisis over 25 years ago, but in one respect it set me back. Like all too many psychotherapists Peck seems to be utterly unaware of dissociation, and implicitly lumps dissociation with psychosis in the class of mental health issues that he labels "major psychopathy". Late in his career Peck even got involved in spirit exorcisms, so I have no doubt that he encountered people who were suffering from undiagnosed and mistreated DID. Reading his books I concluded (in error) that I must have a psychotic part but it seemed that I was able to encapsulate it and stuff it away and keep it stuffed. And in his books I saw no alternative to stuffing it! So that's what I did for over 25 years. And then one day in 2010 the containment failed. Oops.