That is correct.
pdos-generic posits an "ideal bios"
and then uses that.
The ideal bios can be provided by an executable
running under another os, treating the
other os as a glorified bios.
The pdos os remains the same regardless.
It makes the os portable.
Then as of a week ago or whatever there
was a new concept added.
Applications themselves can be run
directly under the bios, not requiring pdos.