Senior Sergeant Tim Crawford of Greymouth police said the fact Mr Bennett had been thrown out could indicate that he was not wearing a seatbelt.
He said they had yet to interview Hunter and would not speculate on what had distracted the driver.
"We have heard Chinese whispers, including the fact he was changing a tape. However, we are not going to speculate.
"We have not interviewed Hunter, and won't for a couple of days.
"All we know is that Mr Bennett was distracted.''
He said it was obvious that Mr Bennett was sidetracked as the vehicle, which was heading north from Haast, had veered across the centre line on to the grass verge, then made a sharp right to try to get on to the correct side of the road, causing the ute to roll.
Mr Crawford said that although Hunter was not badly hurt physically, "emotionally he will be suffering''.
He was treated at Grey Base Hospital before being taken home by his grandfather from Reefton.
"His mum arrived back in New Zealand last night, and she should be with Hunter now,'' Mr Crawford said.
The family moved to Queensland last year and Mr Bennett and his son had returned to Haast to pack up the last of their gear and take part in the annual 'roar' deer hunt.