I think it seemed that you were trying to imply the dropbox's content (not just the public portion) would be visible to anyone.

I am glad this was clarified.

No, definitely not, it's only the public folders and not the rest.

'not shielded': implies that one has to do extra work to shield those. Default is not secure scenario.

'public folder': implies one has to do extra work to make those files public. Default is not public.

I was wondering which one describes Dropbox situation correctly.

Then no one should think it's such a "secret stash", should they? I think using this term is what confused people.