well you have part of it right. The angels (nephilim) did have sex with women and bore them children and they are called gibers (or gibber) which means "different" , and they were different. Great question !! These are the angels spoken of in the book of Jude. They are the ones that left their habibtation and instead of being born of women , they seduced them. This is just one of the meanings of "ye must be born again to enter the kingdom of heaven.