Again, no idea whether or you not your son will end up getting an ASD label but yes, continuing to work on the conversational bits, trying to expand on even his small answers, is the priority. In general talking about how this causes that. One more extreme version that you might related to are kids with hyperlexia.
These are kids, often with autistic features, who read far above age level very early, many of whom who however have very poor compression of what they read. Some, especially those with poor comprehension, go on to develop more autistic features; some, especially those with better comprehension, resolve from their autistic-like behaviors.
Speech language therapy to work on higher order language skills and social skills is a key intervention for those children.