Open relationship, got pregnant

I'm not in an open relationship, but I read an article that was about how some people get themselves in trouble with open relationships. There was a married couple who had an open relationship and the wife ended up getting pregnant by another man. Apparently they kept the baby but the birth father wanted to still be in the picture. I'm sorry but this just seems crazy to me!

I would never want an open relationship first of all and I deff wouldn't want to raise a baby with someone who isn't my husband! Just my side piece. How would they explain the situation in the future to this child?!

What are your thoughts on this?