to be angry: the burning anger of God, which in the Bible is directed only against people for their sin
This word names anger, and in the Hebrew Bible it belongs to God alone. In all fourteen places it occurs, the LORD is the one who is angry: with Moses and Aaron, with Solomon, with the whole nation of Israel, and with the rebellious kings of the earth. When the Bible describes human anger it reaches for other words; this one is kept for God.
The verb is built on the Hebrew word for the nose or nostril (אַף), because anger was pictured as heat and hard breathing in the nostrils. So to say that God "was angry" here is to picture his face set hard against wrongdoing, not a passing bad mood.
Across the Old Testament the word carries a steady, weighty tone. It appears in prayers that plead with God to stop being angry (Psalm 79 and Psalm 85), in warnings that provoking him brings his anger down (Deuteronomy 9), and in the relief of Isaiah 12, where the worshiper remembers that God "was angry" but has turned his anger away. The anger is real, but it is never the last word.