How to create a branch without any links to the others branches

Hello,

I'm wondering how such branches are created in a repository.

For example, how todo, man and html branches from the git repository
have been created ?

Looking at git-branch man, a "start-point:" must be specified if not the
current branch is assumed.

The only solution I'm seeing is to create a new repository with these
'unrelated' branches and pull them from the other repository.

Is this correct ?

Thanks
-- 
Francis