It's international waters, but simultaneously you're not allowed to fly in them? You're not allowed to follow standard intercept procedures in them? I guess China could just claim the entire East China Sea under its ADIZ like the US did off the Pacific Coast and off the Aleutians, but China didn't. ADIZ isn't an internationally protected rule, anyway, so my understanding is that China only does the equivalent of ADIZ intercepts for operators it deems hostile instead of enforcing ADIZ rigidly.