1. c. He states that it spread from the Middle East.
Boccaccio states that the plague "had broken out some years before in the Levant (Middle East) and, after passing from place to place, and making incredible havoc all the way, had now reached the west." This shows that he is aware of the plague's origin and of the way it followed to get to the west. However, there is no indication that he knows by what mechanism it travelled.
2. c. He would find their actions appropriate because he believed human sin may have caused the plague.
Boccaccio does not actually state that he believes the plague was caused by human sin. However, he does think that is a possible explanation (another one would be the influence of the planets). Therefore, it is likely he would have judged the flagellants as prudent and appropriate.
