The real problem for Apple in China is that their brand simply isn't as strong as it is in the US. It has nothing to do with WeChat.
People buy things for multiple reasons. The point of the article is Apple has a problem, one of the reasons, iOS, isn't applicable in China due to WeChat being the dominate platform (and works on all devices).
The author circles back to mention that it doesn't mean Apple is eliminated from that market since they still have other differentiators (status symbol).
The author said that iOS is significant differentiator and that's why people buy iPhones. Except not so much in China now, because WeChat.