It was strange that Siri had gone through that encounter so recently, but that would explain the level of detail with which she told him the story. Luke was still nervous to learn of his father, especially of knowing the things he had in common with the man, but it was good to fill in the blanks on things. Besides, learning about the past did tend to help keep history from repeating itself. But when Siri suddenly stood up, Luke's train of thought broke, mostly because it was so sudden. He frowned a bit, noticing the agitation in her body language. He also felt her presence in the Force, and knew she was troubled about whatever had just crossed her mind.
When she mentioned Palpatine, Luke's frown deepened. He remained on the couch, letting Siri have her space, but he listened to everything she had to say. If Palpatine had been there, then that was trouble. "Palpatine is bad news." Though he had a feeling Siri had learned enough about the future to know that much. It did explain a lot, Palpatine's presence there. It now made sense that he could be the reason Anakin fell to the Dark Side. But of course he couldn't say that for certain until someone from that particular point in time showed up to provide that answer.
Luke followed her thought process easily, and it was very similar to what he was thinking since she'd mentioned Palpatine. "That makes a lot of sense, really. Palpatine is a truly evil man. He's capable of many things, and I would not put that past him." Luke had seen a lot of horrible things the Empire had done, not least of which was the death of his aunt and uncle. He took a breath and let it out slowly. Palpatine was a touchy topic, but he was certain Siri could understand that. He looked at her, understanding her intensity, he felt the same way about Palpatine. "It is always easier to learn about the past than the future." He nodded a bit. "Of course, whatever is said here stays here. I won't mention it again to you, you have my word." And he would hold true to it. There were some things he'd just rather not talk about again, such as the truth of what Leia had told him. He just needed to deal with it and put it behind him, somehow. He had a feeling it was that sort of thing Siri wanted. To be able to fill in some blanks, then let it go.