Did I do the right thing?

So I am 20 years old and my youngest sister just turned 8. Today I came over to my dad's and we set up my inflatable pool and swam and had a water balloon fight. My dad saw my little sister was in a bikini. None of her privates were showing and she doesn't have any boobs or anything yet. He got mad at Sat my sister down and told her bikinis are inappropriate and he doesn't want her wearing them. He said she needs to be modest and not show off her body, not even her belly button. I just let him finish his rant and when he went away and then I pulled her aside and said that she was fine. I said that she is only 8, has nothing to show and that she was fine. I explained to her that when she gets older then yes, she should be modest, respect herself and others, and cover up her privates. She said she would. I told her that when she comes to my dad's to bring a modest 1 piece and modest clothes because it's his house, his rules, but when she is at my home or her mom's that we will decide if she is immodest or not. She agreed and went on to have a good time. I didn't say anything to or in front of my dad so a fight wasn't started and just explained things for her. Did I do the right thing or no?

** I would also like to add so that it is clear. I am more of a parent figure to her than my dad is. When her and my brother come to his home, I am the one that cooks for them, cleans, makes sure they have fun and taken care of. My father sleeps the entire weekend. He does nothing with them or me. He doesn't tech her anything, he barley speaks. He also puts on shows that are sexually explicit and then tells her she can't be like that? Hypocrite. And their mother is a rude ass gold digger. She is always, I mean ALWAYS yelling at them and putting them down. I am the one that makes them feel lived, wanted, happy and everything a child should feel. so no, I'm not their parent, but I would be better than what they have. I'm trying to teach them morals, to love themselves, but also respect for themselves and others. And also, I told her that my dad is boss at his home! And when she is older I told her how important modesty is. I just told her that she is 8, shouldn't feel bad about her body, and that dad being upset with her was just because he loves her.