From the current help text:

$ usage: devpi-export [-h] [-c CONFIGFILE] [--serverdir DIR] [--storage NAME] [--keyfs-cache-size NUM] [--include-mirrored-files] [--hard-links] directory
[...]
positional arguments:
  directory
[...]
  --serverdir DIR       directory for server data. [~/.devpi/server]

The wording does not make clear, which one of directory and --serverdir DIR is the exported data and which the source that the export is done from. From the context, and error messages (if one does not exist), it must be "directory" that holds the exported data. However, with critical operations, there should be no doubt at all.