S3 isn’t a file system. It’s a key-value store. If you’re trying to use it as a file system, you’re doing it wrong :)
Unix directories map directory and file names(keys) to inode numbers(values). And a file's inode(key) is a map to the data blocks(values) on disk that make up a file's content.
S3 might not have Posix semantics but to say it's not a filesystem is incorrect.