You are absolutely correct. Some 5yo children are passive; others are aggressive. At five, the aggressive children need some extra discipline, that's all.
My eldest is so well-behaved and polite that other parents rave about him to me. You would never guess that, at age five, he was a handful. Hitting me, kicking and punching doors, and screaming tantrums that would last an hour was very typical behavior for him.
Reasoning with a five year old might help somewhat, but not much. Labeling him with a disorder won't help at all. Someone needs to be willing to get mean with him, and as years go by, he learns. (As a matter of fact, his behavior was so over the top that I became overly strict, and now he's too timid. So now we're looking into martial arts, just trying to find a balance.)
What disturbs me the most about this story (and others like it) is that the school and the police are taking control, and the parent is not given any control. They wouldn't even release the child to the babysitter she sent.
Most schools want the kids to be mindless, prozac zombies...