The rust resistance of EPS-processed steel strip is superior to that of acid pickled steel strip primarily because acid pickling imposes a corrosion "penalty" on the steel which EPS processing does not. This penalty is a result of chemical reactions that occur after acid pickling and serve as a catalyst for oxidation.  The primary pickling agent is hydrochloric acid (HCl). Although the steel strip is thoroughly rinsed with clean water after immersion in the HCl bath, some residual amount of chlorine (Cl) remains on the surface of the strip. Chlorine reacts very readily with oxygen to form chlorides, so the free Cl acts as something of a "magnet" for oxygen. This mechanism makes acid-pickled steel more prone to picking up oxygen, whereas there is no comparable mechanism at work with EPS mechanical pickling.
In addition to the free Cl, compounds known as "chloride salts" remain on the surface of acid pickled steel in trace amounts, even after rinsing. Chloride salts react rapidly with moisture and accelerate oxidation of iron on the steel's surface. To prevent oxidation of the iron in the acid pickled strip, a thin film of oil is applied to the surface to serve as a barrier between the free Cl, chloride salts and oxygen. No such protective barrier is needed for EPS-processed steel, as no free Cl or chloride salts are present.
However, an additive is used in the EPS slurry blast carrier liquid to reduce the "smut" that would otherwise remain on the surface and dull the appearance of EPS-processed strip. This additive contains a rust inhibitor, a residual amount of which remains on the surface even after rinsing.  It is believed that the presence of the rust inhibitor adds to the overall EPS-processed strip's ability to resist rusting. The additive has been demonstrated to have no impact on paint performance.