It's possible it was just a mistake. But then Alfheim, Vanaheim and Nidavellir are all part of the Asgardian landmass in the comics as well. I honestly don't understand how they decide which provinces are considered part of the Nine Realms and which aren't. But anyway, I just feel like they're going to change this in the films making all the realms actual separate planets, possibly making Nornheim one of them as well. And maybe removing Hel since it can't really be a planet.