Perhaps they're just being nosy. Even though they're avoidant, they might still have that natural human curiosity about what you're up to. It doesn't necessarily mean they want to get back together. They could be in a place where they just want to know what's going on in your world without any real intention of re - engaging in a relationship. For example, if you post about a new job or a new hobby, they might be interested in that aspect of your life from a distance.
It might also be a sign of some sort of unresolved feelings. Avoidant people often struggle with how to deal with their emotions. By watching your stories, they could be unconsciously trying to figure out their own feelings towards you. They could be trying to see if there are any remaining sparks or if they've truly moved on. It's also possible that they're using it as a form of distraction from their own lives. If they're having a tough time in their current situation, seeing your stories could be a way to escape into someone else's (your) world for a bit.
It could mean they're still curious about your life. Maybe they're not fully over you yet and are checking in to see how you're doing without actually having to interact directly.