if 51% of hash power were located in the US, the statement would have been about the US. it is not something special about china that makes this the case, only the fact that it is a sovereign state with the means and will to control activity in its territory, just like every other functioning state. one could also make the case that china might be more likely to intervene in such a way in the economic affairs of its subjects than a liberal democracy, but that is a secondary argument.