Twenty-one young people lost their lives on June 26 at the Enyobeni tavern in Scenery Park, a township in South Africa's coastal city of East London.
Survivors reported a desperate race to escape the suffocating smell.
Relatives of the victims said they were called Thursday to the local health department offices to be told about the results of the final toxicology report.
They said officials briefed them verbally, but did not allow them access to the toxicology report, citing confidentiality.
Xolani Malangeni, who lost a 17-year-old daughter, Esinako, told AFP on the phone that he was skeptical about the findings.
Now the doctor is "saying it's suffocation", he said, recalling previous suggestions that the children had died from poisoning."But it's fake, it's a fake report," he added.
Other parents told local media they were also told that suffocation was the cause of the deaths.
But questioned by local media outside the briefing room, provincial health department spokesman Siyanda Manana neither confirmed nor denied these claims.
A preliminary toxicology report released in July, conducted by a Cape Town lab, was inconclusive. The report found that alcohol and carbon monoxide levels in the victim's blood were not enough to be the cause of death.
The lab also found methanol in the blood of all the victims, which was suspected to be the possible cause of death.
Thirty-one of the pub-goers were hospitalized with symptoms ranging from vomiting to backache, tight chests and headache.
The pub's owner was arrested following the tragedy for allegedly breaching alcohol sale regulations.