tl;dr This is a book about how to make a 2D JRPG in Lua (with a C++ engine). The source code of the engine and the art assets ship with the book.
The project site itself mentions the underlying graphics engine is an Open Source one, but doesn't seem to have info on the licensing for the art/sound assets.
* Over $2500 worth of pixel art (free to use however you like)
But I don't see any concrete licensing statements for the art assets besides that.
Just emailed the author, to ask directly. Will post the response back here (when received) for reference.
> Hi Justin,
>
> I want people to be able to use the art however they deem best so the MIT license is the one I've chosen. Though I don't think I've written this anywhere - which I should address!
>
> -Dan