Well, if it were just about the original books, that would be absolutely fair (and JK mentioning she thought of Dumbledore as having a relationship with Grindelwald would be nothing more than an irrelevant curiosity about how Rowling was thinking about the character).
But based on the ads/reviews, Dumbledore and Grindelwald are both fairly central characters in the latest prequel (where it’s not from a child’s POV), and apparently there’s no hint of any sort of relationship at all - and JK wrote the script. So her continuing to talk about how she thinks about their relationship, while not actually referencing it in any way in the work itself, even when it would be appropriate, is getting increasingly bizarre, frankly.
No, she’s actually the credited scriptwriter for these movies (and the next 3 according to IMDB), not just “based on a story by,” which is what makes this so weird. She could absolutely write in some kind of reference, even oblique, to their relationship, but apparently it’s not in the films.
