Must have been before takeoff?
RVDT,
If you watch the second video from the back seat passenger, you can see they lifted from the front of the hangar and repositioned onto the taxiway before commencing with the final takeoff. The front video doesn't show them lifting from the hangar first. So If the front passenger knocked the mag switch to off with his rifle, then it was likely before the rear passenger started the recording. Though saying that you can't see the front passengers rifle in the second video.
Aside from the video this has been an interesting thread discussion on the magnetos. I'm getting back in the R44 next week so I'll be having a chat with the instructor to have a more in depth discussion on the mags.