The key differentiator is that in China your smartphone can in many ways be abstracted down to the platform that runs WeChat. So Apple's key lock-ins like iMessage and FaceTime don't matter and it has to compete on price.
Apple greatly increased prices in the US/EU also and many of these regions are facing a recession too, but according to Tim Cook's letter those consumers didn't abandon the iPhone. What's unique to the Chinese market? WeChat.