Genesis 4:16 Then Cain went out from the LORD's presence and lived in the land of Nod, east of Eden.
Notice that there is another land and another nation called "Nod". Yet according to most teachings, there are only three people living on earth to this time. These other people upon the earth are those of the sixth-day creation of Genesis 1:28.
Genesis 4:16 And Cain knew his wife; and she conceived, and bare Enoch: and he builded a city, and called the name of the city, after the name of his son, Enoch.
Cain's wife was not a seed, but a woman and offspring of the earlier creation. You will notice a strange thing that starts here and continues through the Scriptures. You are reading the fourth chapter a genealogy of Cain. Then in the fifth Chapter, we will come to the genealogy of Adam. You will not find Cain in the genealogy of Adam, for there is no record of Cain anywhere as being of Adam's genealogy. Remember when even Jesus told us that Cain, the first murderer, was of "his father the Devil".
God gave Cain and Adam approximately the same number of children, and Cain will name his children similar names. The difference is in the name ending "el" of Cain's children, and "ah" in Adam's children's offspring. Most people just skip over names and take their message, and in these latter days can lead you into deception. So this "Enoch" is not an offspring of Adam, but the son of Cain.