The PyPI ecosystem can not, for the foreseeable future, replicate the scope of the conda ecosystem. From microarch builds to library deduplication, conda is a more general purpose solution. That doesn't mean that one "wins out" (and, for reference I predominantly use Python's PyPI), but they're not the same tools.

Does PDM manage C/Fortran library dependencies? IIRC conda was the only solution for managing both native and python dependencies but I haven't really looked elsewhere.

With wheels and the manylinux specifications there's less of a usecase for that, but still could be useful

Not sure about Fortran - but C for sure, yes.

Where does it fetch the C packages from? I always thought PDM was a _Python_ package manager, so the only source is PyPI or another index.

PDM has plugins, such as being able to invoke conda commands: https://github.com/pdm-project/awesome-pdm

Otherwise I don't know what they're talking about, it is indeed a Python package manager.