May have some basis in rules for Victorian modesty, where a woman shouldn't be seen nude by men she isn't going to marry. Since the main character did see her nude, this is usually an indicator that she is the "winner''.
Why does this trope need to have a basis in Victorian modesty? The modern world still has very similar rules regarding seeing people naked. And "going to marry"? No, the Victorian rule would be "already married to"; again, this extends into the modern day (as "in an intimate relationship with", barring extenuating circumstances).
The second sentence seems to suggest that the intent of this paragraph was to expound a theory on how Naked First Impression is used as Foreshadowing, to say that this is the Official Couple. But it didn't say that, and I'm not sure how to modify the paragraph so that it does say that. (It's not my theory, after all.)
I've just removed this paragraph from the lead:
The second sentence seems to suggest that the intent of this paragraph was to expound a theory on how Naked First Impression is used as Foreshadowing, to say that this is the Official Couple. But it didn't say that, and I'm not sure how to modify the paragraph so that it does say that. (It's not my theory, after all.)