This is how cassava flour was made by slaves and indigenous people. In the video, it mentions that cassava flour could be dried using the sun instead of an oven; this is most likely how slaves and indigenous people would dry the flour. They would also use tools made from natural substances such as rock to grind the flour
Source: Pink Angels Kitchen. HOMEMADE CASSAVA FLOUR | How to Make Cassava Flour. YouTube, 15 Mar. 2018.