If this six-year old in question was not autistic, how might he have been disciplined? In this case I assume neither innocence or guilt. But whenever some alleged wrongdoing, no matter what it is, is directed at someone on the spectrum, he's presumed innocent. Even if his guilt has been confirmed, like the computer hacker guy.
I'm not recommending we put the kid in an orange jumpsuit and and shuffle him off to prison, but at least try to find out WHY he was violent. When he's older, this kid could become more violent and increasingly aggressive. I say monitor him for a while, see if there's a pattern of pushing, shoving, etc. You can't really punish a small child in any meaningful way, but you can support him. Support is more useful than pity, someone said. And that's so true.