Sim gained Markteable trait when aging up from toddler

I just aged up my toddler to child age and she gained the marketable trait when doing so (though it's possible she had it before, I hadn't really looked at her traits as a toddler). I never bought it from the rewards store. She also has the Happy Toddler trait, as she should, but the Marketable trait is out of nowhere. Anyone have any idea why this happened?