How can the badminton women's doubles semi-final be China versus China?

There are three pairs of women's doubles players in China. After the draw, all the contestants are divided into two and a half areas, and the winners of the two and a half areas will play the final. Yang Wei/bonita in China is located in the upper half, and Wei Yili/Zhang and Du Jing/are located in the lower half. However, in yesterday's game, Yang and Zhang unexpectedly lost to Japanese players, and Wei Yili/Zhang and Du Jing/respectively defeated their opponents and entered the semi-finals. done