Yeah, git notes are AFAIK stashed into their own hidden branch, referencing the original commit by its hash. That is, the git note points to the commit, not the opposite.
Kind of. The structure is the same and you can check it out if you want, but it's actually a 3rd directory under "refs" - the other two being "heads" (branches) and "tags". That avoids special-casing with trying to hide branches or conflicting with a branch name a user might make.
