Mr Bennett's son Hunter ran in socks back to the service station at Haast Junction to raise the alarm, running through a lonely section of highway surrounded on both sides by bush.
Helicopter pilot Angus Taylor, who later flew the boy back to Grey Base Hospital with a black eye and other minor injuries, described Hunter as "amazing''.
"He knew his dad had not made it. It's a tragedy.''
In Greymouth, the boy was released into the care of his grandfather, who is understood to be from Reefton.
The boy's mother had stayed in Australia but was now flying to the West Coast.
Mr Bennett had lived in Haast township for about five years and was well-loved in the local community. He worked for highway contractor Ferguson Brothers, and at one stage commuted during the week to work at the Stockton coal mine, near Westport.
West Coast police rural senior sergeant Tim Crawford said the vehicle had veered across the road when Mr Bennett over-corrected a steering error.
It ran off the road, through a fence and rolled in a paddock.
Mr Crawford said Hunter would also be interviewed in the coming day, so police could get a fuller picture of what happened, but he praised the "courageous but tragic'' actions of the son in showing such initiative raising the alarm.
Westland District Council Haast-based councillor Kerry Eggeling said the accident was distressing news for the tight-knit, remote community.
He said the community would pull together for moral support - "It always does with things like this.''
