Back when my uncle was in the army, they stored all their weapons dry so the oils wouldn't trap all the dust. So I guess the attic is ok as long as you store it try, or in a gun case or something.
There's enough oxygen floating around in various forms that the _lack_ of an oil layer can allow rust to form. There are other ways to treat it, as your uncle alluded to, but they are probably very sensitive to following the appropriate maintenance schedule.
I went to a friend's house once and fetched a couple of old shitguns from her attic. They were serviceable, but had developed a this coat of rust, enough to require re-bluing.
I believe the heat cycling (heating + cooling + condensation) in an attic acts on guns the same way auto exhaust acts on a car's exhaust system.