If you want to compare numbers you need to know what metrics are used in each. Here is the S&P report that everyone's headline is based upon: https://www.spratings.com/documents/20184/0/ChinasHiddenSubn... While it does not go back to 2012 I see nothing suggesting the kind of increase you are quoting.

It is also difficult to compare the Detroit number to a Chinese city unless we know what are included in the numbers. Detroit doesn't own many of its infrastructure. For example its prison borrows separately, and so does its water and sewer district. Presumably comparable numbers are included in S&P's LGFV total.