Sounds like fuzzy numbers to me. I do the leg raises also and I have had a 6 pack for years. I also do crunches and push ups everyday though, but not nearly as many as that guy claims to do. Not necessary.
Back problems that I have had all can be traced back to using bad form. The knee bone is connected to the thigh bone and so on. If my neck is kinked its because shoulder press was uneven or I turned my neck.
Same goes for squats, I have subconsciously favored my left leg due to a bad ankle...