It's nothing he's said specifically anywhere that I've seen, but it's the impression he gives with the way he talks about her in general (I'm thinking the interview he gave spoiling her death) and the way the title's focus has shifted as it goes on. Like, there was the annual, for example, which was not a Ms Marvel story, it was a Spider-Man story (which he followed up with another issue during this Ghazi arc that was more about Peter than about Carol).
Also, if it's an editorial mandate, it's a bit weird that it hasn't had any effect on her portrayal in the Avengers whatsoever, but then I suppose that would be par for the course ::coughOMDcough:: at Marvel.