If that were true then we would have nasty acid burns from canned soup
and vegetables! When you dissolve salt in water, you get salt water.
Both H2O and NACl are very stable compounds and it would take quite a
lot of energy to make them separate into their elements (H and O or NA
and Cl) which is what would be required to enable them to recombine in
to HCl.

What's happening is the iron is oxidizing when exposed to the air
(which has O2). The salt is acting as an abrasive and removing the
surface rust and exposing iron that hasn't corroded.

I would suggest oiling the surface that is rusting. And not using salt
because it's abrasive properties may remove the oil.

Heidi