"It was just a fluke one of his relatives came along. She (the driver of the car) had gone to park off the road and in that time he was gone - a matter of seconds," Mr Wylie said.
The accident happened about 2.50pm as the boy tried to cross the expressway to get back to Atherfold Cres where he had come from.
Mr Wylie said the 26-year-old driver had seen the boy standing by metal roadside barriers and instinctively began to slow down.
As she drove by the boy darted out to cross from her left. She braked hard but was unable to avoid him.
Within seconds of the impact, and after the woman came to a stop, the boy got to his feet and appeared at her window.
"He told her he was sorry for what had happened."
Mr Wylie said the woman was left "very shaken and upset".
After closing the expressway, police began working to trace the injured boy, and received a call from the medical centre alerting them he had been there before going to hospital.
After being advised he was not seriously hurt the Serious Crash Unit was stood down and the expressway re-opened after about 20 minutes.
"He is very, very lucky," Mr Wylie said, adding the boy would be spoken to later today.
"Crossing an expressway is not advisable," he said.
"It is not a safe shortcut."
No charges had resulted from the incident.