It is just that, as the "Twist of the wrist" DVD seems to have been filmed in the 80's, I remember "dianetics" were very popular then.
Dianetics espoused a theory based on 'bad assumptions' having been ingrained in our brains due to experiences that put us in physical danger (or perceived physical danger) throughout our lives.
I read the book in the '80s, but I remember an example. A small fish is swimming in brackish water finding lots of food and getting fat, but suddenly a bigger fish comes upon him and manages to take a bite out of his fin. It will become ingrained in the small fish's brain that whenever he approaches brackish water, he is in danger, and he must avoid it. This is a bad assumption, as the brackish water might provide the most food for the small fish, and might therefore improve his survival likelihood more than the risk of getting eaten by larger fish. Hubbard called these bad though patterns "engrams".
My distant, and possibly flawed, recollection of Scientology was that by getting "audited" through (apparently lengthy and expensive) Dianetic therapy, one could eliminate these misguided thought patterns and hope to one-day reach the state of being a "clear", which would imply that you had none of these engrams.
Obviously, becoming a "clear" in the purest sense would hold attraction for people whose entire career depends on making split second decisions without any mistakes, like a motorcycle racer. I don't really see what good it has for movie-actors, but I'm sure they get their therapy for free, in exchange for publicity.
Hubbard discussed many different ways that people get these engrams, the majority of which seem related to parental abuse. He claimed that surgical procedures under general anesthetic were very painful events for our subconscious minds, and any speaking or other sounds in the OR would become engrams. He even went so far as to attribute lots of mental problems to being the victims of attempted coat-hanger abortions back in the '60s when abortion was illegal.
I seem to recall some highly publicised lawsuits by parents of Scientologists whose Dianetic therapists had "uncovered" memories of parental abuse that allegedly never happened. I don't know what the outcomes were.
I don't know if Hubbard was right or wrong (or partially right and partially wrong). I might have lots of "engrams" that cloud my judgement, so I'm not yet capable of embracing Scientology. However, I have a hard time believing that Tom Cruise and John Travolta have thought processes that are in any way superior to the general population at large.
Again, I'm not trying to knock Scientology, I'm just trying to present my recollection of what I read in Dianetics, along with some of the criticisms. As I said, I thought a lot of it made sense, up to a point. I felt like I learned some things from reading Dianetics.