I don't understand how the nostr nsec/npub can be tied to my ecash wallet, if I also don't need to have a connected ecash wallet.

Undisciplined

The way is seems, and I'm definitely no expert is, the client that PABLOF7z is creating will make the nostr nsec/npub tied to your ecash wallet. Basically making it so you don't need a lightning wallet or ecash wallet connected to your nostr client. In my opinion this will make onboarding people to the bitcoin network much more intuitive.  