They're absolutely not joking, I've read the novel, ML is Fenrir.
(SEMI SPOILER)
A bunch of things happen and Fenrir gives his human name from when he was a Prince to Elle to settle her in the world and that gets them married bcs she gave him part of her name in the beginning of the story as well. He only calls her daughter bcs it's the 'Fenrir' job to teach the next generation how to be the next Fenrir, but he does develop romantic feelings towards her. Much like when an animal gets a cub and it grows up a good part of them don't see it as it's child anymore but as another adult and treat them as a threat or possibly another possible partner.
Don't get me wrong, I disliked it as well, Elle is not an animal and Fenrir? Well if he remembers when he was a Prince then he's not one either, the logic was just used to justify the creepy situation.

Says romance so who's the ml?
Can't be Fenrir cause he calls her his daughter... Right?