I have another example for you but I have to be careful about the information because it's a child in my daycare but he's kind of similar to your case. The child has fantastic memory and verbal skills and speaks clearly and this all started right after about the age of 1. I was super impressed, but nothing else is coming along, no comprehenson, no participating with the others, slow learning at crafting and anything with simple instructions and he has no empathy or respect for the other children.
He isn't violent or anything, he just always concentrates on what he is doing and doesn't listen to others or respect their space. I'm really exhausted by the end of the day because of this one child and I've been working really hard with him and hoping for progress but not seeing much. I wondered about autism or something here too. But I haven't had any experience with that so I don't know what to think.
It's really great that you are trying to figure out how to help the child but it's really the parent's responsibility.