It's purely descriptive. "Sexy librarian" is a very standard pop-culture image. Also, Kelly Caldwell is female--doesn't mean she can't be into ladies, obviously, but I think you're imagining her as a drooling straight guy.
I did; if that's your opinion, then it seems like you're trying to have it both ways:
On the one hand, you recognize all the subtle implications that are supposed to flow between the details ("dresses like a sexy librarian -> is prepared to handle inappropriate advances"), and praise how they liven the text, and how it is "the entire point" of the medium.
But on the other hand, you're acting like there's some iron law that says the "sexy librarian" description can't possibly sexualize someone, and it's unthinkable that anyone would make that connection, since after all, it has exactly one standard, official meaning, and the robotic readers would never connect it with anything else.
If long-form is all about building up the big picture, why are those implications not part of that picture?
As for what it adds to the story, I think a couple of other commenters have summarized it well: https://news.ycombinator.com/item?id=12466454 https://news.ycombinator.com/item?id=12467125