That's one of the reasons I suspect AGE, not DCS, along with the description of the hit in the neck region (as I had just reviewed my rescue video).
Note from my earlier post here:
"Even swimming to the boat is risky. Most asthma-related accidents happen on the surface because aerosols of salt water can provoke hyperactive airways."
So it may not have been the dive, but the surface swim which provoked the hit.
From DAN, regarding AGE:
Lung conditions such as asthma, infections, cysts, tumors, scar tissue from surgery or obstructive lung disease may predispose a diver to air embolism.
...
Treatment - Call DAN!
The treatment for DCI is recompression. However, the early management of air embolism and decompression sickness is the same. Although a diver with severe DCS or an air embolism requires urgent recompression for definitive treatment, it is essential that he be stabilized at the nearest medical facility before transportation to a chamber.
Early oxygen first aid is important and may reduce symptoms substantially, but this should not change the treatment plan. Symptoms of air embolism and serious decompression sickness often clear after initial oxygen breathing, but they may reappear later. Because of this, always contact DAN or a dive physician in cases of suspected DCI - even if the symptoms and signs appear to have resolved.
Treatment involves compression to a treatment depth, usually 60 feet, and breathing high oxygen fraction gases at an oxygen partial pressure of between 2.8 ata (atmospheres) and 3.0 ata. Delays in seeking treatment have a higher risk of residual symptoms; over time, the initially reversible damage may become permanent. After a delay of 24 hours or more, treatment may become ineffective and symptoms may not respond to treatment. Even if there has been a delay, however, consult a diving medical specialist before drawing any conclusions about possible treatment effectiveness.
In some cases, there may be residual symptoms after a treatment. Soreness in and around a joint that was affected by DCS is common and usually resolves in a few hours. If the DCI was severe, significant residual neurological dysfunction may be present, even after the most aggressive treatment. In these cases, there may be follow-up treatments, along with physical therapy. The good news is that the usual outcome is eventual complete relief from all symptoms, provided treatment was begun promptly.
http://www.diversalertnetwork.org/medical/articles/article.asp?articleid=65
So the victim did the correct thing in being proactive and disregarding the initial doctor's advice
Sounds like he was aware of this risk and acted on his plan, which should help his recovery.