He said it very clearly, and on many occasions. He compared his "tech" with physics and chemistry, and said it was just as precise. He said he was a nuclear physicist. He said he'd done experiments and had evidence. He put an equation in "Dianetics, the modern Science of Mental Health".
Hubbard did not know the first thing about science. Chapter one of Dianetics is total proof of that, to a real scientist. (Nor is that "equation" actually an equation - it just looks like one.) His science fiction has terrible lapses of knowledge and logic. He did study to be a mechanical engineer, but flunked out half way through. He got 'F' in Nuclear Physics.
Of course, a lot of the lower-level tech is common sense, not rocket science. And it is exactly that part that works. The rest of the tech is pretty much Flat Earth. "Touch assists" may have psychological benefit, but Hubbard's explanations about "energy ridges" are out of bad 1930's science fiction. Likewise, his explanations of "mental mass", the Purification Rundown, exteriorization and the like. (Ask me for details.) There has never been a demonstration of "OT superpowers". And even the Church admits that most of the claims in Dianetics are false. Clears do get colds: they still wear glasses: they get old and die. They do not have high IQs or perfect recall. There are no famous scientists (or chess grandmasters) who are Clear. What kind of science would keep publishing claims that they admit are false?
So why do people buy in? Because much of the low level tech works fine, but at something it isn't advertised as doing. It works as a way to install a new belief system in the customer. Auditing with an e-meter is biofeedback training. (Radio Shack sells biofeedback meters for $15, not for $3,750.) Repetitive drills cause a hypnotic trance state. Trance makes you more susceptible and more suggestible. It easily gives "highs", and brief hallucinations such as "exteriorization".
The "suppressive person" theory encourages you to explain your personal troubles with a cheap band-aid: a scapegoat. And, of course, you should "disconnect" from the scapegoat, so that other believers become a bigger and bigger fraction of your personal world. In short, it's not "religious technology": it's recruitment technology.
The important thing is, can I back up what I said? Can I produce, say, biochemistry texts contradicting Hubbard's claims about the Purification Rundown? The answer is yes.
But if you insist on credentials: I have a Bachelors in Engineering Physics, and a Ph.D. in Computer Science. Science fiction, pseudoscience, and the philosophy of science, have been hobbies for a few decades.