For example: is the rocket really "rapidly reusable"? Or is it theoretically "rapidly reusable"?

In the same way that all Tesla's sold since 2017 have the hardware capable of self-driving. Are they really capable of it, or theoretically capable? Until you have self-driving software or have rapidly reused the rocket, how do you know? In the same sense, until they landed a rocket, saying "we have a rocket capable of landing" didn't matter; landing it did.

I may not be articulating it properly, or perhaps I'm misunderstanding how they test these claims.

We assume Falcon-9 first stages are really reusable, right? Not that they are claimed to be reusable, or they are theoretically reusable, but really reusable.

Then the question is, what is the criteria to be really reusable? Would only direct demonstration be enough? Then of course Starship isn't real. If there are other ways to claim real reusability, then maybe Elon's plans are real(istic). Also, historically, Elon claimed something for SpaceX before which later became real.

There aren't currently proofs that Starship isn't possible to create (with parameters similar to stated).