The light seems to travel toward the camera; at 0:27 and 0:28, the foreground gets lighter as the green comes closer to the camera. So there may be something in the sky (rocket? lights of some sort?) that are traveling out of view of the camera, toward it, and lighting up the clouds. Or maybe it's a reflection, as you suggest, Stephen; the foreground lighting and what is in the sky are close in color.
Here is more information from the photographer in response to my questions:
The camera was facing approximately South East.
It was shot on the evening of August 11th leading into the morning of the 12th. No aurora were forecast in South-East New Brunswick that evening.
There is a small airport 25 miles to the North but little or no air traffic going to it that evening. We do see some air traffic going through the shot from middle right to upper left but they were very high and not landing in our province.
The air temp was 12 degrees Celsius (54 degrees Fahrenheit)
There was no unusual weather that night to my knowledge.
The video was taken as a time lapse. Each photo was 30 seconds long with the camera at a high ISO. I took one photo every 40 seconds to create the video. The green clouds in question started to show in the photos at around 2:01 am and ended by 2:58 am.
I wrote to him a bit ago to ask about the foreground lighting; wish I'd seen your post, Stephen, before I sent that off! I've also asked whether he could provide two or three stills.