Corn intended for human consumption is segregated from feed corn from planting all the way through harvest, storage and processing.
While ethanol distillation removes the sugar from corn, it does not remove the other nutrients. You've doubtless noticed from personal experience that corn is not at all efficiently digested. Raw corn fosters a condition known as acidosis in animals when fed in amounts over about 1/2 per cent of body weight per day. This condition is avoided by feeding distillers dried grains.
Sweet corn is the kind sold in grocery stores, whether on the cob, frozen or in the can. Field corn is the type raised to feed cattle, etc, either by combining for grain or cutting for silage. Either way, both are used for human consumption.