One possibility -- in addition to what others have written above -- is that your son is extremely underchallenged, and that he is acting out due to boredom. What really stood out to me about your post is bolded, below:
He had super difficult time in K which is a public school. I still remember he was sent to principle's office almost every week. Then we transferred him to a highly reputable private schools from G1. He had 3 happy years in his private school. The school placed him in advanced reading group in that 3 years but every teacher told me that he couldn't focus on reading material. All other kids could repeat the story but most of time he couldn't. All teachers told me that my DS kept ignoring teachers questions or classroom rules.
Perhaps the reading material at school is completely uninteresting to him, and so, he appears to be "unable" to focus. This could then be responsible for why he can't repeat the story: He never paid attention to the story to begin with, because it was so boring.
