https://exiftool.org/ancient_history.html

    Sept. 26, 2008 - Version 7.44
           - Added read support for DjVu images

There were probably enough systems running perl 5.6.2 around 2008 to cause bug reports, or the code was migrated from an older piece of code and added to ExifTool.

It was not uncommon to manually ./configure, make, make install tarballs locally in those days, especially not on systems like Slackware so I can see it being possible to have old packages installed that were not automagically updated.