I'm none of the anonymous commenters above, but thanks: your explanation makes sense to me, but I also needed this clarification. This part in the rules confused me:

Prompts generally refer to the type of pinch hit you're claiming, not your fill per se. For example, "action movie fandom" would be for a pinch hit requesting a fanwork for an action movie, while "slash pinch hit" would be for a pinch hit requesting a slash pairing

Because I was trying to understand how "not your fill per se" was illustrated by the examples that came afterwards, the grammar read to me as "prompts refer to the type of pinch hit you're claiming, instead of the fill you make". But I now understand from your clarification that the intent is something like, "Prompts generally refer to the type of work you created to fulfil the pinch hit, but in some specific cases (like "single fandom request") they refer to some quality of the pinch hit overall." (Ugh. 'quality of the pinch hit overall' isn't very good.... lucky I don't have to write the rules. :P)