PDD, anxiety disorder, both?

34-month old son diagnosed with PDD by good local child psychologist.  Don’t understand.  My wife and I are socially anxious; my brother autistic.  Mom did IVF, he was early, small, no health issues.  His behavior looks ok at home but "autistic" when not with family/grandma/nanny/aunts/ babysitter. At home, he talks lots, good eye contact, coordinated, climbs, runs, basketball in the hoop. Began speaking at one, advanced.  "Emotional intelligence", e.g., when I stubbed my toe, he looked upset, came over.  Knows when Dr. Seuss characters appear sad, angry, happy.   Not much imaginative play. Occasionally locks onto a toy truck and when I call him he doesn't respond.   Plays with me, share his toys, interact, talk, but very limited play attn span.   Affectionate, hugs.  When we are driving, he points things out. Behavior outside of the house is very different, began at 18mos.  Cry uncontrollably in a few situations, e.g., birthday parties (upon the song). Used to “hold court” with ladies in the real estate office, now withdrawn.  Barber, said, "He got shy". Preschool, doesn’t engage with kids.  At “circle time” teachers put him on their lap or he may run off. More interested in activity instead of playing, eg cooking.  Stares blankly at neighbors or curls up w/ me. Can you be “normal” with the close circle, but otherwise ?  Does PDD = failure to develop social skills w/ peers even if okay in his close circle? Anxiety disorder? Both?