Thanks @viceant for the news. In fact, like @MustardOrMayo suggested, the software shipped with the reader is a blatant copy of KOReader (very old and with a lot of goodies stripped out).
I've reopened an issue
https://github.com/koreader/koreader/issues/5075 to track the licensed material.
Users, be warned, even if you don't care about software licenses. The fact that they're used KOReader as a base shows they probably didn't hire a single engineer over the entire production process.