A zap is a lightning payment that includes a nostr event. Remove nostr and it's just a lightning payment.
Is a dollar bill fungible?
Discussion
Probably comparable to dollar bills yea. I was never arguing zaps aren't fungible or more fungible than on chain. I shouldve been clear my original reply was about on chain Bitcoin. I do think privacy issues hurt fungibility to a certain degree depending on magnitude of the issue - like Moneros sender privacy w/ ringsigs or LN receiver privacy i.e. the way dollar bills can be tracked in a broad sense by serial number, but you never know the "full history" of any particular bill.
I know users say lightning and on-chain are both Bitcoin, and it is, but I don't think that is true in practice i.e. UX, security, trade-offs etc. it functions as it's own thing with different properties VS on chain Bitcoin.