He just seems to seize on unimportant details, and to repeat what I've said to other people who were present the whole time. DS is the master of the obvious.
A simplified example...I'm walking down the road with DD (7yo) + DS (4yo). I greet a friend:
Me: "Hi Ann!"
DS: "Who was that?"
Me: "My friend Ann."
DS: "Who she?"
Me: "Just someone I know."
DS: "Is she you' friend?"
Me: "Yes, she is my friend."
DS to DD: "That was mummy's friend, her name Ann!"
DD: Says nothing.
DS: tugs DD's sleeve, implores her to respond. Starts to get mildly hysterical about getting a response from her.
DD, wearily, eventually: "Yes [DS name], I know!"
DD and DS1 didn't interact like this, but is it just normal for some little boys? DS has to summarise, has to get acknowledged.