Instagram shallowness

The best friend of my boyfriend's ex girlfriend followed me on Instagram today. Her last post was months ago (inactive), and she doesn't follow my boyfriend (how did she even find me?) Am I allowed to think his ex is stalking my photos without being too cocky? I don't know his ex girlfriend personally or her best friend, just that they both exist. Should it matter that she followed me? They broke up over a year ago but in the beginning of our relationship they still spoke. Now, I've set the line for him not to speak with her anymore. I think this might be her trying to see what he's up to even if they aren't talking. But idk! What do you think?