Note that this was most likely written by his facilitator, not by him. It was written via a technique called "Rapid Prompting Method", which appears to be a variant of facilitated communication, a method that has been debunked as simply being the facilitator guiding the child, either consciously or subconsciously, to type things that the facilitator is thinking, not that the child is thinking.
See https://en.wikipedia.org/wiki/Facilitated_communication for more information. I also recommend the PBS Frontline documentary "Prisoners of Silence" (transcript: http://www.pbs.org/wgbh/pages/frontline/programs/transcripts..., video: https://www.youtube.com/watch?v=HXw8Ksvyt5Y), which does a good job both debunking it, and demonstrating why facilitated communication can be quite harmful; there was a rash of incidents in which facilitators imagined sexual abuse allegations from children, leading to substantial repercussions for innocent parents.