Say what?

"I like Generation One Star Scream", says my son abruptly to a mother on her way into the school building to pick up her kid.
"Generation One Star Scream is cool," he says to a peer at a park another time.
Both times, my child who does not understand that the other person does not know anything about his favourite topic Transformer toys, thinks somehow the other person thinks exactly like him. At the moment, he does not talk about other toys, movies, tv shows, computer games or clothes a person is wearing. He does not participate in talking about trivial things that other kids his age talk about - random on-the-spur-of-the-moment-based-on-what-I-see-or-want-to-do-right-now talk. He likes Transformers and thinks its perfectly natural that he should talk about it. If the other person like the mother at the school and the peer in the park happen to not know anything about Transformers, then his initiation at conversation comes to a full stop.
He is at the moment working on the skill of introducing a subject and staying on the same topic of conversation for at least three turns. It's a work in progress. I'm optimistic it will come gradually. Hopefully, once he's mastered the skill, his peers will want to hang around him for a few seconds more at school.