They thought the bible was literal for that matter. They thought the smell of rotting seaweed was ozone and therefore good for you. They thought radioactivity had many health promoting properties. They thought cigarettes were benign. They thought blacks were generally inferior. They thought the a Empire was there to wipe our arse.
They thought a lot of things based on what they had been told.

Yes, but in this case they were right.
We have that on the authority of the eminent, leading mainstream historians who do have access to all the information required.