As long as they are not set to private, I don't see any issue.
Well, I'm not too familiar with Instagram. I did make an account an hour ago, to see if there are songtitles in the stories.
The complete stories can be watched by anyone as long as they are logged in on Instagram - whether they follow InsideOut or not.
However, the links to the individual short videos in the stories can be obtained in the source code, or inspecting the page. Again, sort of 'brute forcing', but not really. (It would be Instagram's fault, I guess.)
So, what do you say?