There is a young child in our immediate family that suffers from autism. There can be circumstances that happen that make him feel "out of control" (often when something out of the ordinary happens) and he will sometimes react to that in an angry, physical way. As far as I know this has never spilled over to affect someone else.
However, my niece and her husband would do almost anything to ensure that this didn't happen. In the example you gave I would have expected one of them to have thrown themselves between you and him, apologised profusely and explained the situation.
On a lighter note, I said to my friend that some visitors to Sussex had been "assaulted" by a child without saying any more. Then I said "guess where it happened". He said Bognor or Littlehampton . My friend is, however, a curmudgeonly old so and so who condemns whole areas/places based on a whim . I have visited both places on many occasions without violence being perpetrated upon my person