Odd indeed. It seems that people that ride a road bike roughly parallel to the the
Camino Frances love to write about it on blogs, forums, write guide books, etc.. I tell people over and over on this board that one can do that entire trail quite nicely on a mountain bike, but that on a road bike they will be looking at an entirely different experience.
I think many of them don't care. They are there for a bike ride, not a pilgrimage, cultural or spiritual, and they are not into mountain bikes. Bikers are a stubborn independant group, and it is often not very productive giving them advice. Maybe that is why no one thought to tell you what type of bike you should have.
When we started the trip in LePuy, there was a huge group of cyclists starting the same day. We worried they would crowd the facilities, until we found they were on road bikes, going 150 km a day. It took us three days to go that far, and from my point of view, we saw 1/10th of the cars and trucks, and 10X the scenery and culture.
Some routes are not so easy on a mountain biking. Some work for very skilled mountain bikers, but would not be good for a first mountain bike tour I don't know about the Norte, but I'd look for a blog or something from someone who has done it.