There are two issues related to scuba related deaths.
The first is more obvious, was there a specific scuba incident such as AGE, barotrauma (ie ruptured lung from holding breath, etc), DCI that directly led to the diver's death.
The other is a concurrent medical condition, seizure, heart attack, etc that happened while the diver was diving. In regards to the latter, a seizure, stroke, heart attack, etc will likely result in the diver's death simply due to the fact they were under water and drowned before they can be brought to the surface. The coroner would likely report cause of death however as drowning with secondary causes heart attack, stroke etc. BTW a seizure would be almost impossible to diagnose even with an autopsy. Not necessarily scuba related except happened while diving.
In regards to this specific accident, any and all causes of syncope (medical term for collapse/fainting) is appropriate. This could be diving related conditions including but not limited to AGE. May be suggested with complaint skin rash but speculative. Could have been previously undiagnosed cardiac condition. Also suggested by reports complaint chest pain before incident but also speculative.
Given lack of specifics any rush to judgement as to the cause of death is pure speculation. Mainly an exercise in "what if ...."
Condolences to the family, regardless of the cause this is a tragic event.