This is such an interesting response, I've never thought of it like that!
What kind of questions are you asking? I found out my kids are advanced because of this and when I asked why they won’t answer me they were like, I don’t want to, that’s boring. Something more advanced and more engaging may help.
It may or may not be focus. My daughter has always done this and now that she’s older I said to her one day, “why don’t you answer when I ask you questions the first time? Are you not listening?” And she,very honestly lol, goes, “no it just probably means I don’t like that question.” So…could definitely be focus, but could also be other things—if he’s very intelligent and he knows you are asking him something he already knows, maybe he doesn’t want to give an answer? Anyway, just to say, my daughter does this and I know she hears me, but it’s not an issue of focus for her. We are working instead on the social piece—I always tell her, even if you don’t like the question, it’s polite to respond, even if you just say “I don’t want to talk about that.”