I would compare this to using something like Spritz (http://www.spritzinc.com/) for a sighted person. At first the higher speeds feel too fast but your brain quickly adapts, especially with daily practice. Given that he's used a screen-reader his entire life when dealing with computers, I'm sure his brain has deeply entrenched pathways for parsing audio like this.

I found that it was easier to catch a few words from that file when I closed my eyes to shut out other distractions. I still couldn't understand much, but I could see how there would be a progression to build to that level.