RS, no, anger isn't part of the diagnosis of autism, though it's often a reason why a few people end up being diagnosed. Autism is social clumsiness plus extreme need for predictability. And often sensory issues on top of that.
The rest is personality. Some react to stress of coping with the disability by being very quiet and people-pleasing, some by getting very depressed, some by getting hugely anxious, a few respond with displays of anger - same as the rest of the population.
Unfortunately, it's usually the angry ones who end up with a diagnosis, as they are the ones who drive people squirrelly and end up being diagnosed out of someone's absolute desperation. So it looks like we're all angry horrible people. Diagnoses are very rare and very expensive, so very few people have them at the moment.
We often do respond with absolute panic to losing a favourite object e.g. a book, though. Why? Because in your brain there's a people-centre that says who's who, how much we love them, what we know about them. And in our brains it's used instead as a storage zone for our things and our specialised interests. If you lose a child, imagine the absolute panic you'd feel, the distress, racing around the streets to find them. That's how we feel if we lose a book etc, because it 'feels' like it's a person who's been lost. Some will 'shut down' in panic, some will cry, some will become hysterical, a few will get angry.
It makes sense because of that brain design problem, but it's weird for other people.
It has a positive side - we are hugely careful with things and data we care about, which makes us excellent at really specialised things. Making a mistake in our jobs is enough to render us speechless with horror - it'd be like us hurting a child of ours if we get it wrong.
We 'rewire' our brains to learn to really love and care for people, by using the older thinner slower brain wiring round the edges. Takes us ages to do, but we can get there. Some sooner than others.
Does that make any sense?