I have a child with autism (same age, too).
With disorders like autism and especially ADHD, there is a tendency of some parents to use it as an excuse. Yes, my son cannot cope in a simple grocery store lineup and will melt down due to his disorder - it doesn't "harm" people, it's just irritating, however, that does not mean that I give him a pass to wilfully destroy property without consequences and harm others. Destroying property is harmful.
ADHD does not mean you go assault people and destroy their property. I do agree she should not have left such an intriguing electronic around a boy with his problems, but his disorder does not excuse violence. You CANNOT excuse violence with children who have ADHD because they CAN learn, it's just far more difficult to teach them. Besides, they don't stay 4 forever.