PDD vs. ASD (sorry this got really long)

I am trying to better understand the differences between a PDD diagnosis and an ASD diagnosis. 

We had our annual re-eval done for our 2 1/2 year old at the private clinic where he receives his OT, speech and day treatment services on Saturday.  He has made huge (HUGE!) progress since his initial evaluation a year ago. His expressive and receptive speech went from 2 standard deviations behind to age appropriate.  A year ago he was considered cognitively delayed.  His score in this area jumped almost 35 points, which the evaluator said was one of the biggest jumps she has ever seen in that amount of time.  

Due to this, they decided to give him a PDD diagnosis, not an ASD diagnosis.  They want to keep the door open for "removal of the label" in the future.  However I am looking back at the diagnostic criteria right now and in my mind, he meets the ASD criteria.  (just for clarification purposes, I am not seeking the ASD diagnosis, I am just confused)

SOCIAL (must meet two criteria)

(a)  Problems with nonverbal behaviors such as eye contact, facial expression, body postures and gestures used in social situations

He struggles with eye contact. It seems that as he gets older and becomes more aware of what eye contact means, the more uncomfortable he gets.  As soon as he realizes that someone is trying to engage him his eyes hit the floor and he won't look back up until they stop trying to engage him. 

Other than me, my husband and my MIL that watches him during the day, he closes his body off to others when in a room with them.  He will hide, push people away and tell people they are too close.  

(b)  Does not make friends like other children in same age group.

At 2 1/2,  I don't expect that he would have actual friends, however he does not enjoy parallel play with same-aged peers and would rather play away from the group.  He does enjoy the company of his 6 year old brother and his friends.

(d)    Lack of social (Consisting in dealings or communications with others) and emotional (characterized by emotion) ?give and take?; Does not respond to social or emotional cues

He does not enjoy the company of others and would never seek it out.  

He still needs to be prompted to say hello, goodbye, etc. 

COMMUNICATION (must have at least one)

(b) If child can speak, cannot start or hold up their end of a conversation (appropriately)

At this point, he does not have any sort of conversations.  He requests his needs and he can answer questions such as "which one...." when shown two options.  He is good at requesting and answering some questions, but we have never had a conversation. He will make comments about the color of things, if they are open or closed, soft, etc.

(c) May echo phrases, words, songs, parts of movies etc. 

Up until a few months ago, all of his communication was echolalia.  This is shifting, but now he is able to at least generalize and echo things in the correct context.  Before he would just say every little phrase he knew that people say in a given context, whether it was relative or not.

(d) Does not engage in imaginative play (as peers)

He will only engage in imaginative play if he is directed to, often he still has a difficult time grasping this concept.  I am really not sure what is expected at 2 1/2.

BEHAVIORS AND INTERESTS (at least one in this category)

(a) Child is so focused on an interest that to remove the interest will result in a meltdown

He is OBSESSED with garage doors and air conditioners.  His brother has the Lego fire station and police station.  Both have garage doors.   If he gets a hold of them, it is almost impossible to redirect him away from open and closing the doors without a meltdown.  He will also turn things like the tri-fold game board from Cooties, or flaps on a book into garage doors.  Again, it is difficult to re-direct without causing epic meltdowns.

(b) Routines or rituals must be followed, they appear to have no function 

As an example, when we go to OT/speech/day treatment, he always wants to follow the same routine to get in.  We get out of the car and he says he wants his backpack, I put it on him.  He then comments on the white line for the parking space and walks down the line.  (he does this in every parking lot, every time we get out of the car)  We walk over to the sidewalk.  There are three sprinkler heads along side the sidewalk.  He touches each one and comments that the sprinkler is off today.  We then walk across the bus entry area to the double doors.  He has to open the doors, or meltdown ensues.   There is then a choice of going up the elevator or using the stairs, he always chooses the stairs for going up. We then walk up the stairs to the check-in area.  As we walk up the stairs, he comments that he is holding the railing.  At the top of the stairs at the check in desk there is a giant teddy bear.  Everyday he walks over, hugs the bear's foot and says it is so soft.  He then stands with his back against the wall in a little hallway, across from the check in desk for his therapist to arrive.  When his therapist arrives, we always go down the elevator, never the stairs.  He has to push the down button and the level one button. 

This is just one example.  There are many routines like this that we are having such a difficult time breaking.  I have been trying to sabotage this particular routine by parking in different places, opening doors for him, etc.  It always ends in meltdown.

(d) Preoccupied with parts of objects

If he is not closely attended to while playing, he always gets stuck on pieces of toys.  Things that open and close or spin are his favorites.  If he has someone directing his play he does OK, but if he starts playing on his own with a toy, he gets stuck and is very difficult to re-direct.

I am clearly not trained to evaluate and decide how these criteria are met and what that means, but to mean, I see so many of these behaviors in him.  I am reading too much into things? We will still (for now at least) get coverage under a PDD diagnosis, so I am not too worried about that aspect.  I guess I am just looking for clarification of these diagnostic criteria and if I am understanding things correctly.  It seems to me, that he meets ASD criteria, regardless of the huge progress he has made in the past twelve months.