Sophie was confused. How did Alden know about her time traveling?

"Sophie, are you going to tell Alden what we actually did?" Asked Keefe. He used her first name. She had listen. "The Black Swan told me what I can do." She snapped. Alden was going to tell her but instead he didn't have time because Fitz had disappeared...

She turned towards Fitz angrily,"This is YOUR fault!" She yelled. "How is it my fault? What is this thing that I caused?" He had her there. Well, first of all, I would have learned it from someone close to me instead of Mr.Farkle, whom I don't know the real name of. Second, your dad is ready to chew us out. This is your fault because you had to disappear for no reason. And then I went to look for you. And then I learned how to do this. Then I got kidnapped and hurt while you just stood there. Is that enough reasons? She was screaming in his head now and he was cover in his ears, like that would help it. "Sophie, stop," commanded a deep accented voice. Another voice, higher pitched, from a boy, said,"Uh, Alden. I wouldn't do that. I don't think she'll hurt you, but I'm feeling some serious rage right now. Plus, I know what she is doing, and I don't want it to happen again."

Now she turned towards Alden and Keefe. "You know, you're lucky I'm not Inflicting rage." Then, she thought of peaceful things. Like when she was finally home safe. And when her friends were near. Like Biana coming and feeding the animals with her. Or when Dex died Iggy's hair and she got a surprise. Or when Fitz sat close to her and keefe protected her, even when they weren't in danger. Then she inflicted them on Alden, Fitz and Keefe. They fell down to the ground. And she walked away, not caring. But she did tell Biana, "You better clean up in Alden's office" and then left.