Because condensation is literally part of the definition of derivative, and basically the weights are a condensed form of the input data. It's some sort of lossy compression, when looking at it from the right point of view.
Summarization and translation are also clearly derivative.
The definition of transformative I found:
- add something new (context of other books I guess, this one might pass)
- with a further purpose or different character (further purpose clearly yes)
- do not substitute for the original use of the work (this one I find difficult. In the case of books, probably. In the case of github, it aims to replace quite some aspects of it)