Greg, Let me share a childhood memory. I guess it was around 1950 hybrid varieties of field corn arrived in Mid. Tn. Funks G 711 was the first variety I remember. Prior to this we planted open pollenated corn eg., Hickory King, Truckers Favorite, etc. are varieties that come to mind. We always shelled corn and took it to the gristmill to have it ground for cornmeal for cornbread for the family. We tried the new hybrid corn for cornbread and it was terrible. In the future we planted the hybrid for our livestock but kept the Hickory King for our cornmeal. With respect to telling the difference between field corn and sweet corn. Generally the stalk is larger, taller and diameter, on the field corn. The ears and grain are also generally larger on the field corn. I would suspect that the corn you are talking about is field corn since sweet corn is more of a specialty crop grown by fewer farmers. Suggest you sample a few ears for yourself.
TK