If this is truly what's happening, then I'm truly happy that he's able to communicate. However, I get warning lights from the fact that this isn't computer assisted communication, this is someone who's moving his hand.

I've heard of similar circumstances where the person moving the hand thought the hand was moving itself, but it wasn't - like a ouija board. It's pretty easy to disprove with a double-blind test, by showing the paralyzed person one picture, the nurse another, and then asking the paralyzed person what picture they saw. In every case, they spell out what the nurse saw.