I don't think so. By that time, Adam and Eve had been long expelled from Eden. Don't assume no more people were created in the outside world just because the bible omits that information. It also doesn't mention the sister you assumed.
There is a lot that the Bible doesn’t cover explicitly. The Bible would have to be the same area of a football field and a mile high in order to cover everything that every human could possibly want to know. Good luck reading that. :)
There are somethings that can only be deduced by reasonable reasoning. Is it more reasonable that Cain’s wife come from a different species or is it more reasonable to deduce that Cain might not have been the only child of Adam to have a problem with the requirements of God and acted on their wayward desire?