Actually, Spinach is one vegetable that will grow reasonably well in naturally salty soil and absorb it into the leaves. Salt is abundant in nature and many things acquire it naturally. Even we as humans are made up of a good bit of salt in our mix.
Beet's, kale, asparagus and Spinach are all considered to have a high salt tolerance. The reason so many people became sick during the last spinach recall was because spinach leaves absorb and holds things from the soil. Maybe that's what your produce guy meant.
But if you have land with a high salt content those are the recommended crops to grow because they tolerate amounts that would kill other plants.
Here's a link with more info....
http://www1.agric.gov.ab.ca/$departm.../all/agdex4246