This is an excellent example of what can happen to older carpet, or carpet that has remained wet for an extended period. It is called delamination, and it is where the glue that holds the backing onto the carpet weave has dissolved and the backing is literally falling off of the carpet. When attempting to extract water or dry carpet like this it can actually disintegrate while you are working with it, so it must be replaced.
Team SERVPRO of Marlboro / Concord ran into this situation at a residence in Westford, MA. The upstairs toilet had overflowed causing a flooding in the basement with standing water. The crew came out and took out the damaged carpeting. They removed the flooring to get to the water damage. Our crew used high tech equipment to clean up the water.