[kmacleod]

Note that there are two ways to look at derivative works.

You're describing a Venn diagram of two independent circles, LibraryA and AppB, and saying AppB does not use any code internally from LibA, share code, modify code from LibA, etc. From that perspective it's not deriving code from LibraryA. You're not wrong.

The other view is two interlocking puzzle pieces, LibraryA and AppB. Can AppB function without LibA? Is there a standard library API that we can swap those libraries out? Can AppB be built or executed if LibA is not linked at build or runtime? GPL operates at this level and is why LGPL exists. If AppB requires LibA, AppB is derivative. If AppB does not link to LibA as distributed and can function without it, but links only at runtime on the user's system, AppB is not derivative.