The word “corn” originally meant any grain, but especially wheat, and is still used in that sense in England. (My English-born husband would speak of the “corn fields” as we were driving through Essex; they were definitely wheat fields and not what we North Americans think of as corn or maize.) In England, our corn or maize is called “sweet corn.”
Thus in the familiar nursery rhyme “Little boy blue” the cow is really into the wheatfield, not a field of corn.
Likewise, when you encounter the word in the New Testament, they are talking of fields of some grain (wheat? barley? rye? etc.), but not the American maize.
The word is being used in an older/broader sense than we are used to here.