The last time China isolated itself from the world they fell back so far that a few gun ships brought down their dynasty. Are they looking to repeat this mistake?
Though the larger point about isolationism is still valid.
The reason China fell back and lost the Opium Wars was not due to isolationism, but rather because for some other reason(s), they missed out on the industrial revolution. But the exact reasons(s) they missed out on the industrial revolution is a great debate, and is the quadrillion dollar question...