I think there is also an element of exaggeration to create some theatre. To anyone who actually follows women's rugby, they would have known Canada were favourites. However, many people wouldn't know that, but would know that NZ are the current champions, even if you could argue they had a lot of luck when they won. They also have a different level of reputation that casual fans would know. Therefore commentators use that to try and create a more exciting narrative even if it's not completely true.