it sounds normal to me, My dd gets told every other day that so and so will never play with her again, until 5m ins later when the other little girl gets her way and does want to play again. my son doesn't tell me as much about it he just tends to play with someone else.
People are so busy that unless we invite they don't do playdates. and usually that does take some time to arrange.
It seems to me that if he is playing legos and kids want to play legos they will play with him and if he is playing cops and robbers and they want to play cops and robbers they will play with him,
I would only be stressed if there was something you are't mentoning and I'm not a mamapedia stalker so i'm not going ot take the time and go back through your posts.
As for names of the othr kdis, if you can volunteer that helps, if not if you bought a yearbook that can be handy for situations like these. Ask him to make a list of all the boys and then all the girls in his class and mabye he will be able to remember the names then.
he just might not want to answer you right when you ask him. try in the car or at bed time.
but i dont thinkyou should worry. Role play wtih him if it makes you feel better.