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

What are your MCCC Pregnacy settings? If you have either "no strings attached" or "random pregancies" enabled, townies and npcs can have babies without you even doing anything. And the third mod you mentioned could have had something to do with it too, but as I don't have that one I'm not sure.

Also, for future reference... we're not allowed to mention that third mod by name because of its adult content.