Since it is a Fantasy TV-show it is in fact on-topic on both sites and it is more a matter of taste where you ask your question (and as you have seen yourself, there are already plenty of questions about it here). Though, if you want some deeper information about the underlying universe or the story of the books, it may be that the people on SciFi & Fantasy have more information regarding that, but this doesn't mean people on Movies & TV can't help you either. As long as the question is not just about the books explicitly, it is perfectly on-topic on both sites.
Look here for further information about overlap between SFF and M&TV:
(As a purely subjective note, I for myself would strongly encourage you to ask it here on Movies & TV.)