Nobody is saying that that they're not related. They clearly are (although the presence of other UI libraries does not affect any comparison of that relationship at all.
Your examples of delegates, responders, targets etc are concepts - and indeed UIKit and AppKit are both built around the same concepts.
The implementations of both is quite different however, to the point that porting something of complexity from UIKit to AppKit involves a lot of tedious changes - or worse: creation of abstraction layers if the codebase is to be maintained for both apps.
Your examples of delegates, responders, targets etc are concepts - and indeed UIKit and AppKit are both built around the same concepts.
The implementations of both is quite different however, to the point that porting something of complexity from UIKit to AppKit involves a lot of tedious changes - or worse: creation of abstraction layers if the codebase is to be maintained for both apps.