Young was driving along Westhaven Drive toward the Harbour Bridge when he saw Hunt in the left-hand road lane about 30 to 50 metres in front of him and travelling about 15km/h to 20km/h.
He said Hunt, who was not wearing a helmet, appeared to get into trouble and veered to the right.
Young said Hunt could have been looking around "even looking to hear or see me, thinking 'I'm on the road probably not doing the right thing'."
"In the process he was thrown over. It was like the rear wheel came up and threw him off which probably told me his front wheel must have locked up in some way, which meant the handlebars could have been locked to one side," he said.