Well-designed cryptographic systems are designed so that you can understand everything about the system and still not get inside.
It's pretty much the exact opposite of security through obscurity.
I think they meant it in a tongue-in-cheek way, as in: my private key is "obscure"?
Only if you're limited to knowing exactly how the actual cryptography works. If you understand exactly how the key derivation works, and know how that is seeded, then you can very much get inside.