That doesn't make the whole of Genesis, or even the whole creation account, a parable. I have looked at several commentators on that verse, and none say that it is a parable. For example, Adam Clarke wrote: "Thou shalt not only die spiritually, by losing the life of God, but from that moment thou shalt become mortal, and shalt continue in a dying state till thou die. This we find literally accomplished; every moment of man s life may be considered as an act of dying, till soul and body are separated."
Also, when we compare the first words of Genesis with one of the parables of Jesus, it is clear that Genesis is a factual account:
“1 ¶ In the beginning God created the heavens and the earth. 2 The earth was without form, and void; and darkness [was] on the face of the deep. And the Spirit of God was hovering over the face of the waters. 3 ¶ Then God said, “Let there be light”; and there was light. 4 And God saw the light, that [it was] good; and God divided the light from the darkness. 5 God called the light Day, and the darkness He called Night. So the evening and the morning were the first day.” (Ge 1:1-5 NKJV)
“24 ¶ Another parable He put forth to them, saying: “The kingdom of heaven is like a man who sowed good seed in his field; 25 “but while men slept, his enemy came and sowed tares among the wheat and went his way. 26 “But when the grain had sprouted and produced a crop, then the tares also appeared.” (Mt 13:24-26 NKJV)