Firstly, it was closed in May. The "General Reference" close reason was only added in April, and the site was only a few months old. At that time we were still figuring out what "general reference" was.
One of the close votes is mine. I also have a comment (replying to a comment that has since been deleted). I assume I voted to close because the "Darmok" part of the question is exceptionally simple to find an answer for. The comment to one of the answers about Kalenda's was added after I voted to close but before I added my comment; if I had seen that first I probably wouldn't have voted to close (and would have undone my close vote if that was possible, which it is not).
There are three parts to the question:
- Who are Darmok and Jalad?
- What is Kalenda's?
- Why is the joke funny?
I still think that the first part is "general reference". Searching for "Darmok" finds plenty of places that summarise the episode of the same name. The third part of the question is tricky, because it's pretty hard to know how much information is necessary to explain a joke - it seems to me that if you know what the episode is about, you can get the joke.
The second part, asking what Kalenda's is, is not general reference, and indeed not even answered, here or on Wikipedia, or on explainxkcd.
This still seems borderline to me: to me the focus of the question is on explaining the joke, and I don't think that you need to know what "Kalenda's" is to do that, so the question is answered just by doing a web search for "Darmok".
However, it seems reasonable to say that "Kalenda's" is an essential part of the question, so I voted to re-open.