I think it is perfectly natural for toddlers to ask questions! I would say that the tummy ladies would not be there because they still live very far away. But then I would say guess what? All the kids there would have been born from a tummy lady just like you!!
I dont believe in lying to kids, so I think you totally did the right thing! And yes, kids talk....but it is nothing to be ashamed of! Your daughter was proudly born for you from a tummy lady because your tummy was broken.....and if it wasnt broken then you wouldnt have her! So you are both special...her for being born from a tummy lady and you for getting to be her mommy!!
Dont freak out! Wear it proudly!!!