My (21f) dad (53m) suddenly apologized for past behavior, and I’m not sure how to respond

Growing up, my dad had a bit of a temper and I had an untreated mental illness. This led to me making a lot of mistakes (not cleaning my room, not taking care of myself in general, not doing homework) and that would cause my dad to blow up on me. I will admit, I did resent him for that for a while. However, I was never a confrontational person, so I would usually just accept his screaming with my head down and move on. As we both got older, I got control of my mental illness and he mellowed out. We’ve never had any problems since and our relationship is better than ever.

Tonight, I was talking about the classes I took this semester, specifically my psychology of learning class. I brought up the benefits of rewards over punishments, not even really thinking about my own childhood as an example, but I guess my dad took it that way. Out of nowhere, he said, “You know, I do regret the way I treated you in the past, I shouldn’t have treated you that way, and I’m sorry.”

I was too stunned to really say much. He was never one to apologize when he hurt my feelings, so I just kind of stood there for a second and then continued as if he hadn’t said anything. But then he said, “You can talk about all the things I did, you’d probably put it into better words than I could.” I don’t know why he would want to do that, but I did what he asked. I acknowledged that he yelled at me a lot and grounded me instead of recognizing that I had a mental illness that needed treatment, and then it was over.

Now I just feel so confused by the whole interaction. I feel like my dad wanted something out of it, but I don’t know what. I didn’t even formally say “I forgive you” and I feel a bit bad about that, but I was so thrown off that I didn’t even know what to say. I want to show my dad that I love him and that I’m over the past, but I don’t know how to do it in a way that’s not awkward. I just don’t want him to feel guilty for mistakes he made a long time ago, because he’s made up for them tenfold by being the best dad ever for the past few years.