South Korea's military said that despite crossing its defense identification zone the foreign aircraft did not violate Seoul’s territorial airspace.
An air defense identification zone is not considered to be part of a nation’s airspace – which is any airspace above its territory or its territorial waters – but instead acts as a buffer zone where countries require foreign aircraft to identify themselves to prevent accidental incidents.
There are no international rules governing air defense zones and Russia does not recognize South Korea’s KADIZ.
China has yet to publicly comment on the Wednesday incident. Though according to a Reuters report, Beijing has argued the airspace is not territorial and therefore open for any nation to use – a stance that echoed comments made by U.S. Naval forces Tuesday after driving a missile cruiser near the contested Spratly Islands in the South China Sea.
I guess China is just flexing on South Korea as a proxy to flex on the US.