While I have no idea of the specifics of this case, I generally frown on the "musta-learned-it-from-somewhere" idea. Even Freud a hundred years ago described the psychosexual issues of young children as being innate.
And Freud was an unstoppable coke freak, non-stop cigar smoker even after half his jaw was removed due to cancer, atheist, personally miserable, who speculated his entire psychological ideas from a small handful of miserable Vienna housewives.
Screw Freud and his idiotic theories, most of which have been proving totally wrong.
Of course all children have innate sexual desires - but usually don't experience much in the way of sexual interest until physically approaching adolescence. Of course there are always a few who are precocious. But extreme sexual interest in a very young children is a sign of having been abused or exposed to explicit sexual situations.
I'm surprised you keep saying it's normal. I've raised children and been around many children. It is not normal.