It could be that they heard something about you from mutual friends and are now curious to see if it's true by watching your stories. For instance, if a mutual friend mentioned you got a new pet, they might look at your stories to confirm it. They're avoidant, so instead of asking directly, they choose this more indirect way.
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.
Well, 'ex' is probably your former partner. They might be watching your stories out of curiosity. Maybe they still care about what's going on in your life, or they could be just nosy.
It could be that they haven't fully moved on and are keeping tabs on you. Or perhaps it's just a habit they haven't broken. Maybe they still care about you on some level and this is their way of staying connected, even if it's in a passive way.