"She undid that, fell on top of me, and then it was a mad struggle to get out."
People who had been in the car behind Henderson ran to their aid, eventually getting Henderson and Rose out through the vehicle's back door.
Henderson said he didn't get their details, but he was very grateful for their help.
A police spokesperson said the driver of the other vehicle initially left the scene, with witness statements that "two or three people" ran away on foot.
But the other driver was eventually found. No charges have been laid yet, as police inquiries are continuing.
Henderson and Rose are now suffering from major bruising, although they count themselves lucky it isn't any worse.
"I've a bruise that's going right across my collarbone and up my neck, from the seatbelt," Henderson said.
"The Friday night, when we were picked up from Waihi, I could barely walk. My knees were shot, my back was wrecked.
"I haven't been able to sleep properly, can barely eat.
Police and the Ministry of Transport have clarified that his death is not considered part of the official road toll, as the road was closed to the public at the time.
Emergency services were called to the annual Mountain Thunder motorcycle event after the man crashed at 12.50pm.