When you say "on this hike" I assume you mean in this same area but on another occasion? No one was injured on this Sierra Club outing. Everyone had a good time!
The biggest mistake people make is just before the Falls. There is a huge, slippery rock. In my photos you can see four young people sitting up there.
This used to be the "trail" to the base of the falls. But if you try it now that it has become so worn and slippery, you almost certainly will fall and will be seriously injured. I have witnessed people fall there twice myself.