It sounds to me like you and the parent poster are actually in complete agreement. They wrote:

    "It's only when those "autistic" traits interfere with
     your life and preclude you from reaching your potential 
     that they're considered abnormal and a diagnosis is apt."

Isn't this exactly what happened with your son? Your son reached a situation (school) where his traits began to interfere with his life and his ability to reach his potential. And at that point, the need for diagnosis and treatment became clear. (Or at least as clear as these things ever are. They're certainly never simple, eh?)

Regardless, much respect to you for recognizing the problem and working with your son to get the help he needs. Not an easy thing to do, but you're doing it, and in an ideal world parents would get medals for this sort of thing. Good luck!