Is this just a coincidence?

During highschool, this girl and I dated during our freshman year, but we broke up and she didn't initially give me a reason why. For the last three years, she would message with me and even stalk me from school, to my work. Despite me bringing up the break up ( she broke us up) she said she no longer liked me and thought I was crazy for thinking she was following me.
Anyway, we graduated in 2016 and I haven't seen her since. But her best friend works at a store near my house that I frequent. And when I first noticed she worked there, she kept giving me the stink eye and would be rude to me, assuming because she didn't like me because of my ex.
Over the last year, she stopped doing that and would be nice and smile at me when she saw me. It didn't even seem forced like she was informed to be nice to me.

To the main point, I recently found out why we broke up, and it was because she was told by the best friend I was stalking some girl and was calling her all the time and a bunch of nonsense. Because of my parents I was only allowed 15 minutes a day to call her when we dated and I couldn't send or receive a lot of text messages to her.

Because discovering this information bothered me, I felt the need to message her and I did. I apologized for the confusion and explained the girl was just my neighbor, and maybe asking her out during my freshman year was a bad idea because I had to beg and convince my parents to let me talk with her. So I just further clarified the situation and said I apologized for messaging her, but I wanted to explain to give myself closure. I sent this message on Instagram.

Suddenly, the friend is now being very rude to me when I go in to shop and she even had followed me around for some reason. She no longer smiles and won't even make eye contact with me.

Could this be related? I haven't heard anything from the ex. And is been going on for roughly six months. Why would this happen and why would my ex not even acknowledge me?
Is this just a coincidence?
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