In China, "districts" are not necessarily part of a city, especially those transformed from counties(https://en.wikipedia.org/wiki/District_(China)). 
"Some districts today are just like counties, with large towns and townships under them governing rural areas."
At the same time, according to the current norms of CN(mainland) communities, a district, regardless of whether it is part of a city, is labeled as place=city (with counties and county-level cities at the same level). Also you can see how widely "districts" are labeled as place=city in China and there's no controversial yet: https://taginfo.openstreetmap.org/tags/place%3ACN=district#overview 