Well, it's hard to say exactly who he is just from this statement. It could be a neighbor who is just being nosy. Or it could be an acquaintance from work or school that has a bit of a curiosity about you. He might also be a family member who is checking in on you in a more modern way, through your stories.
Perhaps he is a family member who wants to keep up with your life by watching all your stories. It might be your brother or cousin, for example. They care about you and are curious about what you're up to.
It could be that he simply enjoys the content of your stories or has a lot of free time and happens to come across and watch them all. However, it could also potentially suggest that he has a special interest in you and is looking for ways to connect with you.
If you don't know him well, it might be a bit strange, but still not really a cause for worry. However, if he gives you any creepy vibes in other ways, like sending inappropriate messages, then you should be cautious. But just watching stories alone is usually not a big deal.