It will be interesting to see what exactly the immediate cause of death was. If he pulled the stinger from his heart the cause of death might be written as,
a. Penetrating trauma to myocardium due to (or as a consequence of):
b. Stingray barb
Here the physiologic mechanism of death might be exsanguination or tamponade.

If the barb didn't go into heart, maybe,
a. Sudden cardiac death due to (or as a consequence of):
b. Stingray envenomation to chest wall
Here the physiologic mechanism of death might be arrhythmia...

Of course they will write the cause of death differently from what I speculate above.

In the late 80's a 12 year old boy died from chest injury. And in 1945 the first known death in Australia due to stingray occured but I don't know the circumstances.