You're right, the fact that they're in China might be irrelevant. I should have mentioned that a very large percentage of mining happens on a handful of pools.
> saying that 70+% of mining happens in China doesn't support the statement
I think the implication is that since China does not have meaningful rule of law, that 70% of mining could in practice controlled by one entity: the Chinese state.
Nor is susceptibility to a 51% attack relevant to that point.