Friend and experienced rider Dave Nicholson and Mr Anderson familiarised him with the machine before the test drive.
Travelling down the driveway, Mr McKenna drove the machine into a fence at low speed. It was not damaged and Mr Anderson then drove it on to the road and Mr McKenna's test-ride resumed.
Moments later and less than 400m away, the machine veered to the left, mounted a kerb and a wheel clipped a concrete fence, causing the trike to rotate and roll.
It hit a power box and went through a smaller boundary fence, throwing Mr McKenna on to a resident's front lawn.
A passerby told investigators he appeared to have a severe head injury and he died soon afterwards.
Mr Anderson said the incident in the driveway was only a "low-speed nudge" and he attributed it to a moment's distraction.
He said he watched the trike driven in a straight line up the street and out of sight. He was waiting for the rider to return when they saw an ambulance go past. Police said examination of the trike showed no mechanical faults.