Does "the left" really support China though?

Not in the manner which you are suggesting. It has nothing to do with communism vs capitalism. It's an oligarchic system where billionaires from China and the West share business partnerships and have overarching goals to have a pacified populace- think of it as an algorithm for power. You can pool the most power by combining populaces/markets and making sure that they are compliant. "The left" favor more collectivist goals and as such are more on board with amoral power consolidation than oligarchs that lean right.