The large stool is what was left behind from the salt water flush. Salt water does a pretty good job of clearing the small intestines. However it does not necessarily clear everything out but also leaves some saltwater behind too. This will flush out what ever is left behind at a later time.
The coffee enema makes the liver produce more bile which is discharged into the small intestines. This creates a contractions which push the remaining solid stool out with the residual salt water.