I think that reference-request is not a meta-tag in the sense that "beginner" is.
If I ask a basic question under "beginner" or "help-a-mathematician", the answer might change slightly in detail, but a non-beginner or non-mathematician could ask the exact same question without the tag.
On the other hand, everyone who looks for the article that introduced superstrings to the literature labels the question as "reference-request". It is a description of the question, not of the motivation of the asker or the type of answer.
If "reference-request" were replaced by, say, "literature-search", would it still be regarded as meta tag?
To give a concrete example (that is not appropriate for this site for other reasons):
Say I vaguely remember that I read a story about explaining friction by little devils and countering every objection by the addition of properties of the little devils and now I want to find this story.
If I wanted to know if the same question has been asked, I would be more certain that the question was labelled reference-request than friction, because maybe someone else only remembered the little devils and the moral for theory-building.
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