Muscle Confusion is a Joe Weider principal.  I'm sure he didn't invent it he just gave it a name and popularize it like he did so many other principals.  It's a simple principal.  Never do the same workout twice in a row.  Change the  weight, change the reps, change the equipment, etc.  Keep your muscles confused as to what they will experience.  I have used it for years.  It's almost a must for me since I workout in a small gym.  Many times the equipment or the weights I want are being used so I just modify my workout accordingly.