I watch George interview on fanfic his main concern is actually not about people who use his work as training their writing but he hates if people making money out his work, fanfiction writers is different with Ai they give george credit, promotion, keep his works and fandom alive main while AI was tool made by people to STEAL other people works without credit and its so unetthical, i don't think George really hate fanfiction when it come to writing he loves the great and My Lady jane He was fine with hbo making fanfiction out his works as long they give him money
Which interview did you watch and when was it published? Because he did at one point hate fanfic.
GRRM didn't like nonHBO adaptive or fanfics of his work (and in general, the writer/artist) precisely because these don't officially enable him to cash checks/enable him to make a living and he thought they'd be infringements on his copyright or be credited, but again, I don't know for sure. NOW, he appears fine with fanfic, whether or not it's from HBO or your "average" Mishka.
The Great & My Lady Jeyne are not his work PLUS they are both historical reimaginings of real events (not a writer/artist's work) that both have been in recent development (not around the time when he openly was against average-person fanfic) AND these aren't his works or came form his work.