Like in: anyone can combine characters. No password is secret?

They are secret. "Secret key" is a technical term in cryptography, and there are thousands of research papers published with this term [0], including a paper by Eli Biham and Adi Shamir on "Differential fault analysis of secret key cryptosystems". Using you believe that you are more knowledgeable in crypto than Adi Shamir (The "S" in "RSA") and insist on using an alternative definition of "secret" not accepted by cryptographers and infosec researchers, there should be no problem using the word "secret".

Otherwise, reductio ad absurdum, Following the same line of logic, all cryptography is "security through obscurity" because there exists a secret key, which is not incorrect. The practice of hiding the design of a system is obscurity, the practice of hiding a specific key to a ciphertext is security, not obscurity, as long as the method of generating and using it is publicly available. If there's nothing to reverse engineer, there can be no obscurity. The method of finding a symmetric key or finding a RSA key is well-known, not obscured, it's simply the size of the problem is not computationally tractable in practice by today's computers.

[0] https://scholar.google.com/scholar?q=secret+key

I guess I don't fully understand this, but RSA works so there MUST be "secret" primes (as in, then can be randomly generated like a symmetric key can).

All natural numbers are computable, and everything on a computer is represented as a natural number, so nothing on a computer can be secret.