I'm not sure what significance engineers have here (who cares what an engineer things about salt?), but even given the hyperbole of marketing which is nothing new (again, surprised this is such a big deal when almost everything is marketed using insinuations, including Morton's), perhaps a reasonable interpretation of "pure" is "devoid of pollutants" (and "salt" understood in culinary terms, not as chemically pure NaCl, but as the naturally-occurring rock salt, with all of the mineral content). Whether the marketing jiggery pokery is true or not, it's a fallacy to attack the salt because of the label.