I talked to Miss Pink's teacher today and she confirmed my feelings that she totally knows what she's doing and thoroughly understands kindergartners (I agree with those who pointed out that curiosity and talking about body parts is usually normal; I just didn't know if that was the case here without being there).
The teacher told Miss Pink that she did the right thing in telling her, and then she let me know that she had talked to the little boy, who was ashamed of himself as soon as he showed Miss P the picture (which wasn't explicit; she said it was basically a "squiggle" of some sort). The teacher talked with him that that was something we don't talk about in school. They were learning the names of body parts and apparently it reminded him of other body parts. So the thing that I was concerned with isn't an issue--I didn't want her to be be the target of that kind of talk all the time.
Anyway, I wasn't all THAT worried even though it probably sounded like it, but I'm glad I touched base with the teacher and that Miss Pink knows she can tell me and her dad anything and we will take appropriate action (or inaction as the case may require). The only other thing I have to say is, God help the boy who ever harms one hair on her head, because her daddy is FIERCELY protective of his girl. And I don't think that's a bad thing for a girl to know.