Actually, we should all feel sorry for Matt. The autism is a mental handicap.
I can understand that an online message board seems appealing to someone with autism. Structured forms of communication: Threads and replies, structure and cohesion.
The trouble begins because it is humans and not robots posting here.
Matt sees some reply from someone, he cannot respond to in a beneficial way, and then he turns to his usual anger and frustration.
Just look at this below definition of autism and think of it in relation to Matt's behaviour: