They didn't have to know any details about diseases and their causes. It's enough if they noticed that people living in the village were getting sick all the ti

They didn't have to know any details about diseases and their causes. It's enough if they noticed that people living in the village were getting sick all the time, while people living outside were not. Apparently 'something' had gotten into their village and it made sense to burn it down and build it up again. And I guess it worked because burning their villages was a way to get rid of disease spreading pests and insects.