User blog comment:APalmAndAFist/Question/@comment-1375848-20201006092808

That's not necessarily anger as such. It was a break in the Autistic's routine, especially if the spill was on a favourite piece of clothing as an example. If the liquid touched the skin that may also have caused something of a shock due to sensory sensitivity and the punch was a reflex action as such.

It's not as simple as saying "it's a symptom". It is far more complicated than that.