This repository redistributes HP Vector Driver which used to be distributed under the Open Printing Framework Consortium (OPFC) project: https://sourceforge.jp/projects/opfc/. Since the original version was distributed under GNU GPLv2, this redistributed version is also under GPLv2. See LICENSE (which was added by the redistributor as the license document of GPLv2 in the original version was an older version).
Contents in the opfc-ModuleHP-1.1.1_withIPAFonts directory are verbatim copies of the original version (i.e. just extracted from the compressed archive).
You can download the original compressed archive file from the release page.