I'm going to put a case here as to why it is on-topic, although I'm the first to admit that the argument is somewhat subjective.
We often talk about physics, engineering, biology, applied maths, organic chemistry, etc. on this site, and the general rule seems to be that you take a concept, and ask a (more or less) hypothetical question that asks the user base to extrapolate their knowledge to a specific scenario, explaining how it might (or might not) actually work.
As I see it, this question is doing exactly the same thing, only with an interpersonal / cultural field of knowledge.
Yes, it's asking about the real world, but it's not asking for a 'fact' from the real world that you could look up on wikipedia. There has been some demonstration of research against the question insofar as there is recognition of the general rules of etiquette and dress in western culture, but this is asking those with deeper knowledge of those rules to extrapolate into a specific case.
This often happens in cases where the answers we give are This is already happening style answers; one could argue that deeper research may have yielded this answer but we accept it because the answer may not be part of what we would call general knowledge. I may well know about the practical application of certain engineering principles that most people have no idea about, but I have no idea what would be considered the boundary of 'appropriate dress' for a 12 YO in England, and under what circumstances.
To that end, the answers that were given were provided by people with superior knowledge in that 'field' and were useful extrapolations of general principles into a specific case that was articulated well by the OP.
In short, my argument is that the question was well worded (and reasonably well received) because it follows the function of questions that are well regarded, albeit against a field or discipline that we don't normally deal with on this site.
I will reiterate that this is just one interpretation of the rules and I think that it's entirely reasonable that other interpretations will be more narrow than this one. I would also point out that this question is on the very edge of what I would consider acceptable for the site and I'd not want to see us field a barrage of questions on hem sizes, turban colours, etc. as a result of letting it in. But, if you disregard the topic and focus on the mechanics, it does seem to fit in my personal opinion.