That was the very first tournament. Which, despite having more prestige, is just like any other tournament. (And they had ArtStyle, for what it matters). If the very first tournament had been a joinDOTA Master, what would you be saying?
Meanwhile 2 months ago, for...I don't know what tourney precisely in which Na'Vi was also participating, I think it was The Defence, aL was just stomping through teams. And I mean stomping. They were literally invincible during that period.
Sure, Na'Vi won the very first tournament of DotA2's existence, a high profile tournament, but that was 6-7 months ago already. Lots of things have changed, both in and out of the game itself. It's like in Tennis ; just because a player won the first Grand Slam of the year does not mean everyone else is suddendly the underdog for all subsequents tournaments.