So far as NOSTR is concerned, a zap is just an event type … representing a chain of events entirely outside of NOSTR.

This is, more or less, just like saying that Bitcoin payments (including those made over the Lightning⚡️Network) are just packets being routed over the Internet.

Technically correct from one perspective, and when constraining the scope pf consideration to accommodate that "just") but actually obscuring rather than explaining salient aspects of the broader picture.

Yes. NOSTR is independent of ₿ and LN. Zaps are just an optional feature and application of NOSTR protocols and some clients.