The problem you are having is that KOReader does not read the Kobo database for the metadata. KOReader is reading the metadata in the OPF file in the ePub. What you have to do to fix this is use the Calibre editor and edit the metadata in the OPF so it is correct. Then KOReader will read the correct metadata.
What you could do it go to the KOReader Github and put in a request for KOReader to read the Kobo database.
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