Nabisco Premium Saltine Crackers boast on the box that they are "topped with sea salt." Isn't there a geologic sense in which ALL salt is sea salt?

The definition of Salt is fairly broad, with many compounds making up salts, many of which are inedible to humans. A good example being Lead Acetate. https://en.wikipedia.org/wiki/Lead(II)_acetate which is made without any nod to the sea. https://en.wikipedia.org/wiki/Salt_(chemistry)#Properties

Common Salt (NaCl) is almost always derived from sea water, although often having been deposited underground and eventually pushed to the surface over several million years.

https://en.wikipedia.org/wiki/List_of_edible_salts

So ALL salts, no - but all edible salts - mostly. Things like MSG and Ammonium Chloride do not come from the sea, and could be used to flavor your crackers, but they'd certainly taste different

The main source of non-oceanic salt would be continental salt lakes (like the Great Salt Lake or the Dead Sea). However, even the salt in these closed land basins comes from the weathering of rocks. Rivers carry those dissolved minerals down into the basin. Because those original rocks were often formed by ancient marine sediments, even lake salt usually has a prehistoric oceanic connection.