Dash cam footage of the event shows a silver sedan passing Reti's car on his right, before it drives past a big truck moving in the opposite direction.
The sedan's sunroof then visibly lifts into the air, twists around and then appears to shatter.
Shards of glass fly through the air before appearing to hit Reti's windscreen.
In hindsight, Reti believes the slipstream of a passing truck may have caught the edge of the sunroof, hooked it, and lifted it off.
The motorist in front of him carried on for another 100 metres or so before pulling over. Reti followed suit, jumping out of his car to survey the damage.
The driver of the car, which was now missing a chunk of it's roof, appeared to be in his 30s, Reti said. His 3-month-old baby was restrained in the backseat.
Neither party appeared to have been injured in the incident.
"He says to me, 'did that hit you?'."
"And I say, 'look at my windscreen'. There's cracks in my windscreen, scratches on the car, all that kind of thing."
Reti said speed didn't seem to be a factor in the incident - he believed it was simply a freak occurrence.
Reti had a friend in the passenger seat of his car, who he said was shaken by the incident.
Both were "immensely" thankful everyone was unscathed, Reti said,
"Even at the normal speed limit of 100km/h, you have projectile glass and a sunroof coming at you - that's got momentum."
Reti had continued on to the awards, while the other driver continued on, sans sunroof, in the rain.
He assumed the motorist's next stop was the mechanics.
"There was no choice ... you can't have a car with a hole in the roof."
