So when you tap on a Story, before it loads you are shown a warning that indicates that the Story author will see that you viewed it.
Story authors will be able to see who viewed, and this is a fair compromise for Follower-only Stories.
For Public Stories, I'm debating logging views as the context isn't as meaningful.
Instagram only does this when you open a story directly by its URL (e.g. someone sent you a link). This makes sense because you don't always know where links lead so the confirmation prevents any inadvertent exposure to the story author. But when you tap a story in the UI, it's a conscious action, you already know that you're opening a story and that doing so would expose you to its author.