I'm guessing the reason those workers looks so serious is that the photo was taken using ambient (dim) lighting, and would require a long shutter opening. They would have been told to hold still and not even twitch. Also, being photographed would have been a pretty rare occurance, a hundred years ago. They would be in awe of the process.
Or perhaps it was a chemical flare, flash photo, and they were trying hard not to blink.
All things considered, it's a darned good photo.