For someone (actor) to do something (theme i-) in an angry manner.
Imbūngot Wīgan di inatnan himmāpit at timmā'ot nan tatāgu.
What Wīgan did in speaking he did in an angry manner and so the people became afraid.
Ibūngot: focus is on an action or deportment, as speech, facial expression used to express anger. Occurs as part of a verb chain, see Grammar Sketch 7.19.