How can one sim get another pregnant and never have met?

So yesterday I was playing the game and decided to play the Harris family from Eco Lifestyle. I had played with Gemma Charm previously and she met Jeb Harris in highschool. They aged up together, and were buds. And I was gonna cheat him into University. And once I played him I saw that he had a daughter not in his family. However the daughter's mother was not in his relationships anywhere. So I spent a long, very long, time searching every world to find her. So he could meet his child, and the child's mother.

Now when we first saw her in the family tree she was single. And had the last name Cho, so our daughter had the last name Cho. By the time we met, she was married and had the last name Shimizu. Confusing, she was also a 4 star celebrity.

So somehow he met, woohood, and had a baby with a celebrity all without every actually meeting her. Or introducing himself. And she went from single to married in 5 minutes.

Now I have Basemental, MCC, W, and Nisa K. How did this happen? Like it's okay, the baby is fine. We added her to his new family with the gf he met later on. And like other stuff happened. But I still wanna know if all the other sims that I've been seeing, that the game autopopulated, that have babies, don't know the partner.