The word incensed is used here to describe God's feeling after observing the actions of humans. Considering that it was what caused him to later decide to punish all those who decide to defy him, we can assume that he was angry with humanity.
It also helps when we check the meaning of the word in the dictionary: "Very Angry, Enraged".
Incensed means "To be made angry". As in, humanity made got very angry.