I am the original poster of the question. The logic that was originally used to argue that my question should be deleted seems to be that (a) there are other, non-StackExchange sites where I could (should) have asked my question; and (b) the question is not relevant to this specific StackExchange site.
To respond to both these points in turn: (a) seems to fail immediately, because there are many StackExchange sites that replicate the functionality of a more "official" site. https://drupal.stackexchange.com/ replicates https://www.drupal.org/forum, or example, and https://apple.stackexchange.com/ replicates https://discussions.apple.com/. Many people tend to use the StackExchange sites instead of the "official" sites because of the extra functionality that StackExchange provides, and because of the active StackExchange community. The argument of "there is an official site where that question should be asked" doesn't hold water, if we accept those two StackExchange sites as offering a precedent.
The second point seems to be that my specific question it not relevant to the Writers StackExchange site, since it refers to a writing tool rather than the act of writing. This might hold water, and it's up to the Writers SE community to decide where it sets the limits on what is an acceptable question or not. As I'm not part of that community, I'm happy to accept whatever it decides. However, it should be noted that I did search StackExchange site-wide before I asked my question, and questions related to Scrivener occurred more in Writers SE than they did anywhere else. Indeed, Writers SE has a Scrivener-specific tag. If the Writers SE community decides it doesn't want to deal with questions relating to writing-specific software (as opposed to more general word processors or desktop publishing software) then it might like to consider where in SE these questions should be asked, as by default people seem to be coming to Writers SE for help with Scrivener.
Finally, a general point that I think applies to almost all sites on StackExchange. The way my question was dealt with was pretty abrupt. Someone could have explained to me, in a friendly way, that I had asked my question in the wrong place, and then helped me find the right place to ask my question. Instead, the comments initially started talking about closing the question. This doesn't bother me personally as I've used SE for quite a while, and I know that that is how things are done here: but it will put off less experienced users. Being friendly doesn't cost anything, and it it is an essential part of building a community.
Incidentally, I had already asked my question on the official Scrivener forum, but hadn't received an answer. I thought I would give SE a try, as often I find my questions are answered really quickly here. I note that the user who initially wanted to close my question has stated above that "If I can find an answer on their support site why can't the questioner". @Monica Cellio's response -- that some users are just better at using Google than others -- is right; I'd add that the user who wanted to close my question has not directed me to the answer he's apparently found.