According to #29874 this package was renamed to par2cmdline because it installs a binary with this name, but it doesn't (at least, not anymore). Upstream call it parchive, and it's also known as parchive on ubuntu, fedora etc. so for consistency it would be nice if Gentoo used the same name.
Correction, on Ubuntu par2 is this app, and parchive is what gentoo calls par. Maybe it should've been named par1/par2 after the upstream branches after all..
It seems to me like `parchive' is the parent project name which produces a number of different par-related tools, including `par' and `par2cmdline'. These both exist in Portage and seem to fetch the correct source matching their name, so IMO no issue exists here.
Comment #2 seems the most correct one here
