Scout overheard a conversation among the members of the Idlers' Club. What did she learn that put a "different light on things"? Why did this confuse her?

Scout overhears the men in the Idler's Club discussing her father and the trial. Through listening, she learns that her father was "appointed" to defend Tom Robinson..... that he didn't have a choice in the matter. This confused Scout because she couldn't understand why her father hadn't told them about it, and also because it made no sense that people were mad at him when he had no choice.

“Yeah, but Atticus aims to defend him. That’s what I don’t like about it.”

This was news, news that put a different light on things: Atticus had to, whether he wanted to or not. I thought it odd that he hadn’t said anything to us about it— we could have used it many times in defending him and ourselves. He had to, that’s why he was doing it, equaled fewer fights and less fussing. But did that explain the town’s attitude? The court appointed Atticus to defend him. Atticus aimed to defend him. That’s what they didn’t like about it. It was confusing.