Your question reminds me about the time when I put my webcomic in the slice of life/all ages section, then I realized my characters may swear occasionally and there might be younger kids who'll read it. So I put it in the slice of life/comedy section instead.
Nah, I don't think swearing should be included in mature content. I think that category is meant for violent and sex scenes that are very graphic. But if you want a peace of mind, you can clarify with a moderator on that one.