The entire photo is the finish line. Look at the color of the ground -- it's cream, the color of the lines on the track, while the track is blue. Each vertical line of the photo is taken in the same position on that finish line.

The first "line photo" is the right-most column of pixels on that photo. The next photo is the second-to-the-right column, etc. This way the winner can be determined as the line first photo that has the contestant's torso in it.

Nowhere, the camera takes an image of a single line in time (and what the camera sees is the canonical finish line). The visual finish line isn't where that camera is looking, so it's never captured. The left and right of that camera isn't space, it's time (right is earlier, left is later).

I had the same question, "what happened to the track?" I appreciate you asking it.

On second viewing, you can see that some things are very distorted and this is obviously a composite as has been explained.