So when writing "it" as "den/det", you don't have to match it in gender with the thing you're referring to? I wrote "Det er en and" just to see and was marked as correct. That's really cool if that's the case.
It's not exactly a "rule," but people are often associated with the common gender. Both "et annet" and "en annen" mean "another," and although it's ambiguous, "en annen" implies the object is a human being without any further context.