[Travis Nunn]

This was a common trick with the old Cirkut camera. In a large group photo there would be a "runner" at one end who would be standing at the starting point of the shot and would run behind the group to appear at the other end of the shot when the camera completed its travel.

I suspect Bridges is just using a camera that takes longer to make the exposure than your Horizont.

There are quite a few school class pictures out there where someone did just that