There are different opinions on this matter. We do not know our history and much is hidden and hushed up.
I know buildings in the city that have floors underground, which used to be at least the first, and now they are below the basements. There are buildings in which the first floor has been excavated and it is below the ground level.
There was some kind of cataclysm in our history, and perhaps these drawings were made shortly after it. We just don't know and find it hard to believe.