Moody's downgraded China credit rating for its own interest.

Basically, Moody's wanted to impede the success of China-HK bond trading link as it didn't participate in the US$9.5T China bond market.  Moody's downgrade of China maybe for a political reason too.

http://www.cnbc.com/2017/05/17/china-hong-kong-bond-trading-scheme-approved-by-regulators.html

There is no convincing reason to downgrade China credit rating while USA maintains AAA rating.

http://www.reuters.com/article/us-usa-ratings-moody-s-idUSKCN0S11AM20151007

USA has a national debt of USD$19.85T without many foreign reserves.

http://www.usgovernmentdebt.us/

China has a national debt of USD$4.3T and USD$3T foreign reserves.

https://en.wikipedia.org/wiki/National_debt_of_China

USA debt-to-GDP is 106%.

http://marketrealist.com/2017/03/how-big-is-the-us-debt-compared-to-other-nations/

China debt-to-GDP is 41%.

https://en.wikipedia.org/wiki/National_debt_of_China

It looks like only the USA can take on debts but other countries cannot because USA is the only resilient country in the world.  Therefore, other countries will collapse if they take on debts because they're not resilient.

Does this make any sense at all?

I hate it when credit rating companies give biased ratings.  US credit rating agencies tend to give better ratings for USA companies.  Just look at Lehman Brothers credit rating given by Moody's before the big collapse.

http://www.huffingtonpost.com/2009/09/30/credit-rating-agency-anal_n_305587.html