How does it distinguish between the Boolean value false and the string "false"?
Good question. From the man page, looks like boolean values map to a file with contents either 'true' or 'false', while NULL values map to empty files.
According to https://mgree.github.io/ffs/ffs.1.html, it tries to autodetect the type (so false will default to a boolean) but you can explicitly specify the type via extended attributes.
Very interesting though it’s just reinventing the database wheel