If I understand correctly, he has a form of autism where he can’t speak. They also may have been making fun of Pokèmon with this, since it was still very new at the time, but I doubt it.

Growing up there was a very autistic boy in my elementary school, and all he could do was kind of moan and yell and laugh.

I will point out that Timmy does talk in post COVID and can speak in people’s minds in Coon and Friends.