There is efficient arbitrage between the Chinese and non-Chinese exchanges. If Chinese miners sold their coins only in Chinese exchanges, that would tend to depress the price there. Then the arbitragers would immediately move those excess coins to non-Chinese exchanges, until the prices got equalized.
You may be right - I wouldn't claim to know enough about the subject to be able to put forward a coherent argument one way or the other.
However :-
a) the arbitrage is not
that efficient between East and West- it was only a couple of weeks ago that there was $50 difference between Huobi and Bitstamp, Chinese BTC being at the premium, and
b) it has been said that the diametrically opposite position (re. China/BTC) is the one being held by the Chinese than the one you have posited - that is, they are prepared to take a loss in Yuan just so as to be able to convert to USD and so shift "value" out of China.
I dunno.