One could say that people in a coma with low brain activity should also not be able to know what's going on around them, but some who've come out of comas relate that they had some awareness.
Anyway, I'm not really clear how awareness of one's physical surroundings says anything about life after death. I suppose they're implying that their soul was hovering above the table watching the goings-on, I don't know, but why can't they simply be underestimating how long the brain remains functional?
To me, evidence of life after death from NDEs would consist of, "I went into a white light, and I saw my Uncle Joe, and he told me I was going to live, and he asked me to ask Aunt Susie about my long-lost half-brother that I never knew about, and then when I woke up, my family confirmed that they were keeping this family secret from me."