It could mean a lot of things. Maybe they're just curious about what you're up to. Or perhaps they still have some feelings for you and are using this as a way to stay connected in a small way.
There's a chance they blocked you in a moment of anger or impulse. And now, they can't resist seeing your stories because they still care about you, at least on some level. They might be too proud to unblock you directly but still want to keep an eye on you.