I think she was just passing on information with things to work on.
I am noticing a lot of parents seem to think when a teacher notices and tells them these things, the teacher is judging. She is just informing.. You do want to know her observations? Especially compared to the rest of the class?
This is going to continue all the way through High School, so just take it as information.
And yes, children this age, do begin learning how to say, May I play with you Or Would you like to play with us.. This will be very useful when they begin school. Some children that have never been in daycare, preschool, do not have these skills ans are a little behind on their social skills.
Practice sharing at home. May I play with that red truck that you are holding? If he says yes, say "thank you".
If he is building blocks, Can I play with you and the blocks?
In the bathtub, may I play with the bucket? Can we take turns pouring the water?
I wanted to play with that puzzle too, when you finish, can I play with it?
The other thing is if he is around other children, if he wants to play with the toy another child has give him the words to ask to share or to play with the toy when the other child is finished.
Share your snacks, ask if he will share his snacks. Make sure he sees you and dad sharing.. use the words, pleas and thank you with each interaction.. It will feel forced and redundant, but this will sink into your sons vocabulary.
These behaviors have to be taught, especially if he does not have siblings or playmates at home. He will catch on.