Nope, I didn't forget I wasn't clear but that sentiment was from before that reveal in chapter 7. But it is a detail I wouldn't be surprised if anyone forgot. It hasn't been made a major part of the story yet, just a single piece of lore. It was mentioned multiple times that the current princess was originally the successor before Elle's appearance but it was mentioned only once that it's the role given to the females of the royal family. If you forgot this single piece of information, then it's easy to not think of Fenrir as being female.