"A man paralyzed from the neck down due to a spinal cord injury" typically can still talk.

If not, there's blinking/mouth controls like Stephen Hawking.

Surprised at how far I had to scroll to find Hawking's name. If he were still with us I bet he could type circles around this guy.

It would also be easy enough to make him memorize some text and attempt to replicate it, would it not?

No. You’re trying to measure whether the machine is accurately translating his thoughts into characters. He may make errors in spelling or memory. Success is whether the machine spits out the characters he intended, even if they weren’t the ones he was supposed to send.

Same way autospell is not working with 100% accuracy and you're still managing to express yourself, I believe