This Bible contradiction is from the Skeptic's Annotated Bible.
No, they knew that God spared the town of Zoar.
Genesis 19:21-22 View context
And he said unto him, See, I have accepted thee concerning this thing also, that I will not overthrow this city, for the which thou hast spoken.
Haste thee, escape thither; for I cannot do any thing till thou be come thither. Therefore the name of the city was called Zoar.
Genesis 19:31 View context
And the firstborn said unto the younger, Our father [is] old, and [there is] not a man in the earth to come in unto us after the manner of all the earth: