How is it possible that with a diagnosis of mild intellectual disability i was able to learn english so well that i became billingual? also i learned to read first before my classmates and impressed everyone?

Having a mild intellectual disability does not mean you don't learn or retain what you learn, It means the rate at which you learn or the ability to retain is less than the expected speed or amount understood. You can get to a ripe old age and know more than your pears who quit learning along the way.

The mild intellectual disability may not affect language skills but may manifest in other areas of cognitive ability. It is better to focus on your strengths than on the label of "mild intellectual disability" Wish you good health and success in your endeavors.