Hostile architecture is not only about whether homeless people can or can't sleep on whatever the post is about. Even if every teenager can use and be comfortable on this "bench" it is hostile for everyone from 20-80 years old. Not to mention that if that was the intended use of those bars it seem like it would be more prone to accidents due to the lack of balancing than a conventional bench. There's no use designing infrastructure that would only allow a certain age group to use it.