Why was I put in special Ed classes in elementary school?

The more I think about it the more I wonder. Why was I put in special Ed classes from 1st to 4th grade? At the time I never realized that it was a class for autistic students but I definitely could see the difference between me and the other students. There were students that would flash the class. And there were students that would throw full on tantrums in order to get there way. I was a very well behaved kid my main flaws were I was lazy and didn’t like to be told what to do. After the 4th grade they told me I “ graduated” from the program and was transferred to regular classes mid school year. I continued my lazy ways in regular classes making my grades awful. This would lead to me going into a learning program threw out 6-7th grade only to be “graduated” again. I would proceed to take high school seriously averaging As to Bs in almost all classes. My strengths were history and English. Contrary to my poor writing and punctuation skills. I made my way to one of the highest levels of history and English classes by my senior year of high school. Why was I beaten down all my past with the shadow of thinking I was autistic? I feel I am normal I have no social problems other than mild anxiety. I’ve never been told I’m autistic by family or a doctor. I’m also very well educated on history now a days being able to compare in knowledge in quite a few topics with historian friends I have. Why was I always seen by the school system as slow and unintelligent it’s like they didn’t know how to teach me.