At the end of Chapter 2 Flavius Josephus Antiquities of the Jews says Seth built the Great Pyramid before the Flood. This is apparently the source of this false information. The Great Pyramid was built after the Flood not before. Josephus was a false teacher.
"They also were the inventors of that peculiar sort of wisdom, which is concerned with the heavenly bodies, and their order. And that their inventions might not be lost before they were sufficiently known, upon Adam’s prediction that the world was to be destroyed at one time by the force of fire, and at another time by the violence and quantity of water, they made two pillars: (13) the one of brick, the other of stone: they inscribed their discoveries on them both: that in case the pillar of brick should be destroyed by the flood, the pillar of stone might remain, and exhibit those discoveries to mankind: and also inform them that there was another pillar of brick erected by them. Now this remains in the land of Siriad to this day."
Titus Flavius Josephus (/dʒoʊˈsiːfəs/; 37 – c. 100), born Joseph ben Matityahu (Hebrew: יוסף בן מתתיהו, Yosef ben Matityahu; Greek: Ἰώσηπος Ματθίου), was a first-century Romano-Jewish scholar, historian and hagiographer, who was born in Jerusalem—then part of Roman Judea—to a father of priestly descent and a mother who claimed royal ancestry.
He initially fought against the Romans during the First Jewish–Roman War as head of Jewish forces in Galilee, until surrendering in 67 AD to Roman forces led by Vespasian after the six-week siege of Jotapata. Josephus claimed the Jewish Messianic prophecies that initiated the First Roman-Jewish War made reference to Vespasian becoming Emperor of Rome. In response Vespasian decided to keep Josephus as a slave and interpreter. After Vespasian became Emperor in 69 AD, he granted Josephus his freedom, at which time Josephus assumed the emperor's family name of Flavius.
Flavius Josephus fully defected to the Roman side and was granted Roman citizenship. He became an advisor and friend of Vespasian's son Titus, serving as his translator when Titus led the Siege of Jerusalem. Since the siege proved ineffective at stopping the Jewish revolt, the city's destruction and the looting and destruction of Herod's Temple (Second Temple) soon followed in 70 AD.
Flavius Josephus, Antiquities of the Jews — Book I
Chapter 1, verse 1: "He also placed a cristalline [firmament] round it; and put it together in a manner agreeable to the earth; and fitted it for giving moisture and rain, and for affording the advantage of dews."
Chapter 1, verse 4: "God therefore commanded that Adam and his wife should eat of all the rest of the plants, but to abstain from the Tree of Knowledge; and foretold to them, that if they touched it, it would prove their destruction."
Jeremy: Josephus was a Jewish historian and not a Christian. His interpretation of the Torah is incorrect showing it was the work of a fallible man. He does confirm that the scriptures prove there was a firmament protecting the earth before the Flood, made of some kind of crystalline material most likely ice? But when he says fitting it for moisture and rain he is wrong. The Bible says it did not rain before the Flood.
And when he says, “abstain from the Tree of Knowledge; and foretold to them, that if they touched it, it would prove their destruction."
Wrong. God said not to eat the fruit. It was Eve that added and we must not touch it. And God did not say it would be their destruction, but rather they would die spiritually, and later gradually die physically. And it would not be only the destruction and death of men, but for all life on earth and cause entropy, causing things to deteriorate.