Looking at the flying map, I would say China shot it down because they claim Congsan's pilot flew in "their territory".
China uses the philosophy "kill one scare a thousand". and scare the all stupid, rotten Congsan communist party. After shot down the jet fighter, then they invaded the sea under "Rescue Mission Flag", and Congsan says "thank you for your generosity and help" haahahahahha
It is a joke of the year because China ship collided to Vietnamese fishing boat on the side try to sink and kill the fisher men. Now, China offers to rescue. What's the F@@@.
What a shame for our country because stupid Congsan's leaders.