The difference is in that 2nd bracket section.
The context is that MPI is a specification for message passing parallel compute framework.
openmpi is a implementation. openmpi is installed.
boost.mpi is a C++ Boost library that can hook up to openmpi or other mpi impls.
Fedora handles this with some RPM macro magic somewhere. I think you’ll have to use and/or emulate that as needed. I wasn’t seeing it by the wiki page below, but asking of the discussion forum may find someone more familiar with the mechanisms.
It may require building the RPM on a Fedora box or Fedora chroot/container. There may be some Fedora additional macro configuration present when built in a Fedora environment.