Why did my ex boyfriend's sister follow me on instagram?

Anonymous
Last night while I was on break I posted on my instagram story and I went and looked through who seen it and I noticed my ex boyfriends sister looked at my story and she doesn't follow me and I don't talk to her either. Then a few minutes later she followed me on instagram and I requested to follow her because well, I don't have anything against her. I just think it's kind of odd because I'm not on good terms with her brother and I don't talk to him anymore and he doesn't follow me on instagram because I removed him by blocking and then unblocking him and he doesn't have me blocked and my ex dumped me and I'm pretty sure his parents made him dump me because they didn't like him dating and he was so happy with me and a few days after we broke up he told me that he wasn't over me at all. Can somebody help me? I've never had this happen before so I'm kinda curious lol..
Why did my ex boyfriend's sister follow me on instagram?
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