Ah I was wondering why you can't actually see the finish line in the image. This wasn't really described well. Are the shadows of the runners artificial then?
That’s also the reason for the distortions. It’s not a single frame taken at one time.
As the runners' shadows cross the finish line, they are recorded by the camera in the same way that the runners are.
The shadows are what's projected on the line from the stadium lights, and the shape is how they changed in time.
Again, not well explained in the article.
This short video might be a better explanation of the "line camera" concept of multiple photos of a single line being stretched out over the x-axis :