And by what metric is China considered a communist nation?

It's headed by a Communist Party along the principles of Marxism-Leninism with the goal of using Socialism with Chinese Characteristics to oversee a Market Economy and build up their productive forces to achieve full socialization of the economy.

If you have an hour and genuinely want to know, read China Has Billionaires. It isn't a fully socialized system, but it does use Central Planning extensively, and the Party is in control of the Bourgeoisie, not the other way around.