Speaking to the media outside Dubbo court in NSW, Ricky Hampson Sr said it has been hard to hear the "huge list of mistakes" that cost his 36-year-old son Ricky Hampson Jr, his life.

"How do I feel? I feel angry. I feel frustrated," he said.

Mr Hampson Jr died after a misdiagnosis by staff at Dubbo hospital on August 14, 2021, prevented him from getting the treatment he needed to save him.

Doctors at the hospital treated the extreme abdominal pain he presented to the hospital with as if it were a rare marijuana-induced condition. However, it was later found out the pain was caused by lacerated ulcers in the stomach.

Mr Hampson Jr's family believe he would still be alive today had he received a correct diagnosis.

Speaking before a coronial inquest on Tuesday, February 27, Dr Sokol Nushaj - the senior doctor on shift in the emergency department the night Mr Hampson Jr came in for care - admitted "cognitive bias" played a part in the fatal misdiagnosis.

"He admitted that his diagnosis was influenced by his own biases and diagnosed Dougie with a drug-related condition, cannabinoid hyperemesis syndrome, something the doctor claims he sees a lot in 'Aboriginal people' at the hospital," Mr Hampson Sr told the media.

"The doctor now admits this diagnosis was completely wrong."

Giving evidence, Dr Nushaj said he came to the impression Mzr Hampson Jr had the cannabis related condition when he was first wheeled into the emergency department, before any examination had taken place.

Mr Hampson Jr had smoked cannabis on the afternoon he visited hospital, however, did not have the nausea or vomiting normally associated with cannabinoid hyperemesis syndrome.

He also told nurses and a junior doctor on shift, Dr Lisa Hu, about a "popping" or "tearing" he felt before the sudden onset of pain, which they wrote in his medical notes.

Dr Nushaj said he was not made aware of the information and did not read the notes.

Mr Hampson Sr said he was frustrated that his son had done the right things when presenting to the hospital and explaining his symptoms, only to have the information disregarded.

"The senior doctor has admitted that 'popping and tearing' is a sign something is seriously wrong and should have been investigated. But it wasn't and they failed him," he said.

"What else could my son have done to get the life saving treatment he needed? A hospital patient should be able to describe their symptoms and then expect to be properly treated by medical professionals.

"Why didn't this happen for Dougie?"

Pressed on their memory of the evening that Mr Hampson Jr stayed at Dubbo hospital by counsel assisting the coroner, the nurses and doctors who attended to him could not recall many of the events.

"The doctors and nurses who've given evidence have said that they 'don't recall' important details about my son's last hours, and the details of the treatment provided that potentially cost Dougie his life," he said.

"How dare they forget my son. My family has relived and gone over every moment of Dougie's last hours in painful detail for the past three years.

"Why do they get to forget, when we must remember everything?"

On Wednesday, February 28, Dr Nushaj rose in the bench to offer a formal apology to Mr Hampson Jr's family who had gathered in the gallery to watch the proceedings.

"I wanted to say to the family that I'm very sorry for your loss and I wanted to say that I wish I could go back and change things," he told the court.

"It was a mistake and a tragic outcome that will sit with me for the rest of my life."

Before he could make his apology, members of Mr Hampson Jr's family - including his sister and father - walked out of the courtroom. His partner and children remained in the room.

"My family and I walked out because we don't want an apology, it's too late for that. I've been hearing 'sorry' my whole life," Mr Hampson Sr said.

"It's time to move past sorry. We want change."