I think he probably wasn't disfellowshipped based on what you have said. This is because his family is still communicating with him after moving out of the family home and he is going to a convention. I think its unlikely he would go to a convention if he was disfellowshipped, particularly if he is not attempting to come back. Even though he is not disfellowshipped, it is entirely consistent with current JW thinking that all his friends would cut all association with him outside of meetings if he is living a worldly life - not going to meetings, having a 'worldly' girlfriend etc.
Honestly, I think the fact that he is going to a convention shows that he has not firmly rejected the belief system. It sounds like he is still indoctrinated, at least to some extent. He may want to live a life outside of the religion on one level, but the belief system will likely still be there under the surface, and unless it is destroyed, there is a strong likelihood that he will feel pulled back.
An experiment to see his level of indoctrination. Get him to go through the site https://jwfacts.com/. Ask him to read it and be with him when you do. Ask him what he thinks of the various articles. Talk to him about them. I think his reaction would be instructive. If he is resistant to read these articles or rejects the information without properly considering it, then it shows he still has a high level of indoctrination and in his heart he has not really left the organisation.