It's a way to spread out the highest ranked players. I'll explain it this way which should make a little more since. (Example using 4 sections)

So first put the highest ranked player in section #1,
2nd highest in Section #2,
3rd highest in Section #3
4th highest in Section #4

At this point you start to go backwards.

5th highest in Section #4,
6th highest in Section #3,
7th highest in Section #2,
8th highest in Section #1,

... and again, in the other direction.

9th highest in Section #1
10th highest in Section #2
11th highest in Section #3
12th highest in Section #4
... and so on.

Hopefully that will make more since seeing it when it applies to more section. With only 2 sections, it does look a little strange.