This author is only talking about people who's EEGs have flatlined. No electrical activity taking place in the brain at all. Granted, the equipment has not become necrotic or you're correct, we couldn't get them back. So this is the experimental universe we are limited to.
Part of the problem with trying to figure this kind of stuff out is that one of the things our brain truly excels at is filling in the blanks. The brain has to backfill data constantly (like every time you detect motion for one example since the optic center actually sees stills) and could easily be doing that in response to an NDE. Or the signals may have gotten too slight to detect. Or the doctor could be right.