1)
What is the relevance that they won due to Hashem's anger at Yehudah?
1.
Malbim: When there is great anger to destroy, Hashem hands them over to cruel people. When anger is tempered with mercy, He hands them over to their brothers, whose nature is to have mercy on them. Elokei Avoseichem gave them into your hands - you all have one father and one G-d (so be merciful, like brothers).
2)
Why did he say that they killed with great anger?
1.
Malbim: You did not act like messengers of Hashem's Hashgachah, rather, amidst hatred for them, without mercy on your brothers. This is not how Hashem wanted to punish them! Their cry reached Shamayim due to this.
