If your definition of rust is iron oxide, then you are correct. Chrome plated brass does oxidize
once the chrome plating starts wearing exposing the brass underneath. Even chromium is not impervious to salt water
...eventually it too wears off exposing what is under it.
Stainless steel has some iron content. The cheaper stainless steel has a higher iron content....therefore the red corrosion
you occasionally see.
Stainless steel pop rivets can go active...start oxidizing. What causes some stainless steel parts
to go active and not others, in virtually the same place and same application, is beyond me. If one bolt out of a few has gone active, I just replace that bolt...or whatever stainless steel part it is.