When I was around eight years old, I began to have anger issues. I had outbursts, would call people names, and would even hit others. It came to a head when I slapped my grandmother in front of my family. My mother took me to a therapist and after three or so months I was much better. She didn't conclude I was Autistic for some reason, but that's a whole other story.
My son avoids conflict. He only hits himself if he's stressed out & overwhelmed. He's never had any angry outbursts or anything like that. I try to keep a very positive, calm & relaxing environment for him at home. I don't take him out to public places (except he attends school) because he has an extremely difficult time. I am teaching him how to order what he needs through shopping apps for delivery. I am still learning about Autism & my son so that I can know how to help him, teach him, prepare him for living independently & parenting him. I talk to him about what I can do better & how to help him. He's been responding positively to that approach. I think that's helpful for him to not have to be in a position to be frustrated or angry.
I’ve found that frustration due to the lack of ability to verbally communicate needs leads to anger issues for some ASD kids. I’ve learned over the years that anticipating my son’s needs or things that lead to frustration help tremendously towards avoiding anger. Once I learned my child’s triggers it became easier to avoid things escalating to the point of anger & physical aggression. In some cases I think extreme anger can also be triggered from too many stressors or sensory sensitivities that kids are bombarded with in certain environments. I don’t think anger issues are a strong indicator of being Autistic though. Anger popping up at the age of 8 could stem from so many different things, & not easily seen as being related to being Autistic. Since therapy worked so quickly for you it’s possible that your anger was related to something specific & resolved. Hope this helps.