[LamaOfRuin]

Except that the author then goes on to say how much they would prefer the derivative works to be open source, so it seems like they do want it but have been convinced they shouldn't. AGPL and an offer that other licenses would be available on request seems perfectly suitable.

[pcthrowaway]

The author doesn't say they prefer derivative works (e.g. works using a library) to be open source, only that they want modifications to the library to be open source