First, and perhaps most important, your daughter would be interviewed by an expert who very gently elicits information from her about what might have happened.
There are no behavioral changes and her behavior towards the man in question has not changed at all. I have no idea why she said this and my feeling is that it is completely innocent.
She is also at the stage where she is very interested in what a penis is and what a vagina is – she occasionally can be found on the floor probing her vagina.
Several clues are associated with sexual abuse as opposed to normal development (but many children give no clues except what they say): Hopefully, nothing significant happened to your little girl, but if my daughter came to me with the same story I would not let the situation go uninvestigated.
The scenario you have described is the most frequent way actual abuse is detected.
Adults and older children hold a position of tremendous power in their lives.