The only Joesephus I could find relating to this was during the period after Jesus' crucifixion. Perhaps I found the wrong person, this is likely.
He says however that the pillar of brick should be destroyed. Neither has been destroyed so I don't see how this applies. Both are said to report "many scientific discoveries and inventions, notably in astronomy" but this does not seem to be the case.
In the second link you supplied I read the following paragraph and this seems to blur what you are trying to say even more :
William Whiston, a 17/18th century translator of the Antiquities, stated in a footnote that he believed Josephus mistook Seth for Sesostris, king of Egypt, the erector of the referenced pillar in Siriad. He argued that there was no way for any pillars of Seth to survive the deluge, because the deluge buried all such pillars and edificies far underground in the sediment of its waters.
The flood, I am told, created the depth of the Grand Canyon in sediment, raised Mount Everest from level ground, and shot water from the depth of the Earth into space - but it did not affect these two monuments? Granted the Sphinx was buried in sand for quite some time, but certainly not to any depth I would expect given what I am told the flood did to the rest of the planet.
You had previously stated that the Pyramid was an altar, not a pillar created to survive a flood for the purpose of preserving knowledge.
IE: I still do not understand why these two monuments are evidence of a pre-flood society or that the flood took place at all.