Joshua Mamet is just too good-tempered. He didn't get mad when Aria Grant blamed him, and even asked her about her situation very gently.
"Oh, what I was doing just now doesn't matter. The problem is you called me several times in a row. What do you want to say? If you're just calling to ask what I'm doing, then I'm really gonna be angry."
Aria was very calm when she said all this, as if she hadn't just been angry when she said those words.
"Why would I call you for such a boring thing? Clearly, it must be something important. I've found some leads in my investigation. I think we can start with the forces trying to break up the Flack family. It seems they're not all in agreement, and I've found someone named Thomas Yates who often disagrees with the older members because he's younger."
So, Joshua Mamet was calling her to tell her all this, Aria realized Joshua was thinking about her problems too, but Aria's tone was still a bit uncontrollable.