I think it's an off-by-one SDK bug in playdate.file.listFiles. If I give it a directory with one file, it just returns "../". If I add one dummy, it gives me rdk.json and not the dummy file. Reported upstream here: https://devforum.play.date/t/playdate-file-listfiles-only-showing-some-files/356...
If it gets no response, I'll open a new bug rather than reply to an old one.