I agree that it there is so much overlap it is difficult to tell. As a therapist, I always look at symptoms when the person is in their fitting environment, not when they are in an environment that doesn't match. Many gifted kids are going to have social deficits in a typical classroom because they don't think the same way as most other kids. If you observe him in a group of equally gifted children and he still is not interacting well, then you may be looking at ASD. You can also look at the MCHAT assessment and think back to when he was 2-y/o and if he matched some of those characteristics for ASD before a same-age peer environment was an issue.
