Did you think that Burton cleared the matter up in the chapter? He seems to have a respect for what is not known, and this makes him present his conclusions tentatively, which I actually appreciate.
He does make a good case, I think, for this feeling of knowing being in fact a sensation: "Sensation strikes closer to the neurophysiological truth of a relatively discrete output from localized neural structures..." (38).
Since he believes that the feeling (or sensation) of knowing relates strongly to what we call conviction in everyday life, he thinks that genetic differences in the area of the brain responsible for the basic sensation of knowing may account for why some of us take easily to conviction, while others of us don't. Seems logical.
He tells us that by stimulating the brain, we can only produce certain feelings or emotions, the ones considered primary. So we won't find a patient expressing shame or arrogance during this kind of procedure. Conviction, though, he seems to say can be produced. This would classify it, or at least its primary component, as a primary emotion. Don't know about that.