Giovanni,
As you said, pickling is the act of removing the oxides that restrict the oxidation in the atmosphere from working with the stainless steel chemistry to form the chromium protective surface that is necessary to prevent rusting. After pickling, the surface is now considered as passive. Actually, "passivation" is known as decontamination. The passivation liquid is applied to the steel as the last step before shipping. It "reinforces" the passive surface by removing any smudges, contaminants, free iron, etc. from the surface. This is explained in the Avesta Weldiing Manual. I agree with what you said, but possibly I just said it in a different way.
Chuck