The difference between Curated Lists and NIP-51 lists, if I understand NIP 51 correctly: each NIP-51 list has a list owner, who controls what items go on the list.

With Curated Lists, each list has an author, but there is no list “owner” bc the author has no more control over the items on the list than anyone. Anybody can submit items to any list. And then the submitted items get accepted or rejected by the web of trust that is centered on the reference user.

And you can select anyone as the reference user. Different reference user will (potentially) mean a different set of items on the list.

(In the absence of controversy, you’ll probably get the same set of items regardless of reference user. But when there’s controversy, then you’ll see changes in the list depending on reference user. I refer to this phenomenon as Loose Consensus.)