It is because Apple has been dominant in the premium smartphone market for years, including in China. Huawei have started to make a big dent in that tier in China after eating Apple's lunch in the lower price categories.

This is a feature that Huawei brought to market before Apple, which was kind of a first. Until recently, they were just following Apple's innovations. It's early and I wouldn't want one now, but I wouldn't be surprised if smartphones-that-fold-out-into-tablets was the standard by the end of the decade.