There’s nothing sudden about what China’s been doing with its trade surplus. In the aughts they were spending most of it on US treasuries. After the great financial crisis they began tapering their purchases and shifting to a basket of other currencies. In the mid 2010’s they started the belt and road initiative to turn trade surplus into loans and infrastructure in foreign countries. It’s been at least 15 years of them pulling away from the tight coupling they had with USD.