Without looking at the code, I assume each file is stored as a binary blob with a hash, snapshot and volume id. This would allow you to keep identical files only once.
The last paragraph is conjecture. However the idea is that the filesystem is arranged so that it only stores the difference(or a different version) of the file.
Which doesn't sound like either content addressable or a union filesystem. Unless it's using the filenames as indexes in which case I guess it is content addressable, but has a serious flaw in that you're limited to only one unique filename:content pair per filesystem.
Without looking at the code, I assume each file is stored as a binary blob with a hash, snapshot and volume id. This would allow you to keep identical files only once.
The last paragraph is conjecture. However the idea is that the filesystem is arranged so that it only stores the difference(or a different version) of the file.