Did someone call me? / Didn't someone call me?

1. Did anyone call while I was out?

2. Did someone call while I was out?

My book says 1 has no expectation while 2 has. i.e) the speaker expects someone called him.

Then what about this?

Basically, the sentence follows are different .

3. Are you coming.

4. Aren't you coming.

My question is this.

5. Didn't somebody call me this afternoon?

6. Did somebody call me this afternoon?

My book explains the speaker of 5 expects a positive answer.

I made up 6. I think number 6 has the same meaning as 5, hasn't it?

Is there no distinction between 5 and 6?