I'm just like him. My fiance tells me not to do things all the time and I just forget. I have the worst memory. Someone could be talking to me and two seconds later I can forget what they said. You might need to get him to look at your face and say "listen to me" because if he is hyperfocusing on something else he could be responding without even knowing there was a conversation at all. I do that, I will have talked to someone without realizing it, just because I may have been reading something interesting or thinking about something else.