The deaths were deemed cannibas related because on autopsy, no other cause could be determined. One may have had an undiagnosed heart condition; however, as such, and with no previous issue causing him to seek medical attention, the cause of death being inhalation of excessive amounts of THC was listed as causing cardiac arrest.
But it doesn't matter, previous health aside, if someone Ingests or inhales something, bringing about death, the cause of death still is the ingestion or inhalation of said substance.
Having worked in an Emergency Room, I know that as much as people love to argue that cannibas is harmless, the medical evidence does not back it up. I've seen people in restraints from cannibas-use induced paranoi and psychosis. I personally know a friend who after smoking a high quality strain of Kush, got severe paranoia and ran out into traffic in fear of the "things chasing him. Luckily he did not die. And no other substances were found on his tox screen.