Hard to see due to poor picture quality, but based on what I could see, it seems like a spontaneous pneumothorax to me (based on the lack of lung marking on the left compared to the right side).
Therefore, since the lung is deflated, all you would have in the left side of the open cavity, which would make the left side hyperressonant.
So the xray was similar to this
this is a large volume gas emboli (which you would expect from a diver due to nitrogen precipitation). You can kinda see it in the xray overlapping the heart shadow/left diaphragm.
This is a giant pocket of air, basically so I just figured it would be hyper-resonant due to hyperinflation.
As you go below sea level, there is an increase in atmospheric pressure. Increase in the pressure may cause rupture of subpleural blebs leading to pneumothorax.
Not sure if this is entirely correct though.