IMO this is the first such attempt to hijack a plane
Perhaps, but in the past China has gone to great lengths to suppress any news covering their internal security issues. They have ongoing challenges with the Uyghers (a Muslim ethnic group in Western China), and some Uyghers (very few) have established ties with Islamists in Pakistan and Afghanistan, but that distorts the real issue which more similiar to the ethnic/cultural conflict/tension China has with Tibet.

Over the years there have been several bombings in some parts of China (buses were a popular target). Who knows what else is going on in this regard. This may be the first hijacking attempt, but I wouldn't be surprised if it wasn't. I doubt we'll ever hear the full story, or Paul Harvey's "the rest of the story" about this episode.