If you check out MTF at the time, there was a mayor sensation that Delpo could do it, because he has proven beforehand that he could and was growing and getting gradually better and better throughout the year. It wasn't a fluke, Delpo showed he was progressing in solid steps that year. So we all felt Delpo had a chance at the Fedal wall, specially against Nadal.
I wasn't on MTF at the time, but I remember several analysts predicting JMDP to get to the final by beating Murray and Nadal. I don't think many expected him to actually beat Federer in the final though, I know I didn't. Making the final was hardly a surprise, taking down Federer there was though; although he had been mightily close at RG months earlier, beating Federer in your first Slam final at 20yo is a quite impressive achievement.