But he's not schizophrenic. And schizophrenics very much appear to be having a conversation with the voices, not "talking to themselves." He is reassuring himself and narrating his life, not responding to voices that only he can hear.
We have to go with the facts of the case, but my source on schizophrenia is a decade of research on schizophrenics and doing 20 years of field diagnostics, mostly of schizophrenics. I did 2 years of fieldwork in inpatient wards for schizophrenics.
When a schizophrenic responds to voices, it very much sounds like someone being on the phone (although there's often a lot of unusual affect in the responses, as opposed to the flat affect otherwise seen in many schizophrenics). BK never mentions hearing voices in any of his TapATalk missives, which go on for a couple of years. We are allowed to use what he says there. He describes a specific auditory disturbance (which can be part of VSS) and another person responds that they have the same auditory disturbance, but it's not hearing voices.
This is self-soothing and I'm guessing that since childhood, his parents have used those words to soothe him, he has internalized the parental voice and is now soothing himself.
The narration-of-ongoing events is also seen in perfectly normal people. I've never witnessed a schizophrenic narrate their ongoing life events. I've seen schizophrenics pause conversation to listen to their voices, but never have I heard one report that the voices are soothing. The very fact of the existence of unseen people speaking in a room is anxiety producing, not soothing. I also know schizophrenics as colleagues (high functioning schizophrenics) and two of them have been helped by medication (to not hear voices) and the third has grown accustomed to them and ignores them (kind of the way VSS sufferers have to do with their snow).
So it's POSSIBLE that he could be hearing voices, but so far, I see no evidence of it and am going with what has been permitted to be discussed here, as it is the best guess (BK's own account is compelling).