Earlier quoted context omitted.
Yep, that's what happened. Also, procedures were different back then, so we could have many more siblings, hope we didn't hook up in college.
The percentages I've heard are all over the place, but a decent number of children are actually not genetically related to their fathers. (I've heard anywhere between 3% and 30%.) One theory that's been postulated is that women have affairs to increase the genetic diversity of the sperm that compete for her egg, thereby increasing the chances that her children will have good genes.
The fact that men are often actively trying to get in women's pants likely has a greater effect on these statistics than women's genes' desire to reproduce.