recent advances in medical science are built on previous advances which are built on advances that preceded THOSE advances....

in a lab, to test a hypothesis you do an experiment.
trial and error.

it is how we have acquired scientific knowledge.
I think it is important to understand that.

ultimately, all medical knowledge has been acquired through trial and error. also, the article doesn't say anything about what they "actually did know", it only make suppositions about what they might have known or done.