Sweetie,
She was serious.
The JOKE is on YOU!
I suppose the ‘ah, fan fiction’ remark passed you by?.
Understand that and you will grasp her irony.
Considering her quote about the fanfiction community....
We all know that Harry Potter is a HUGE fandom when it comes to people basing fanfiction stories on it... including compromising situations that are sexual and gay (not necessarily in the book but that people imagine these characters doing).
Rowling is WELL aware of these online communities and fans that do such things with her creative characters and is a bit against it since she is concerned about a child google-ling some fanfiction that is innocent in the HP fandom but then coming across an unprotected NC-17 piece and ruining their fragile minds.
Same thing happened with Lord of the Rings, Viggo Mortensen and Orlando Bloom ‘pushed the envelope’ for a joke by teasing some fans and were then driven them up the wall when they found out the “interesting” situations people wrote their characters into.