They beat G2, Astralis, SK and FaZe, let's look into these matches a little bit more.
Astralis: first tournament with device since he's gotten back from the hospital/being sick, obviously they're not going to be in good form.
G2: Very inconsistent team, play like a top3 team some games others they play like a tier 2 team, not to mention C9 lost to them in groups (16-8) overall okay win
SK: they had a stand in which they barely practiced with maybe once (maybe) not only this, they just came out of a bo3 against Fnatic the match went 2-1 for SK so very close.
FaZe: I can't say this wasn't a good match it was super fun to watch, overall a good match.
But atleast 2/4 teams were not at their best.
Then in cs_summit, C9 lost to Liquid who just got a new player, basically two new players counting steel, who came out of a bo3 against Sk, not only this They had a 1-0 advantage. I just decided to put this to emphasize C9 is inconsistent and not a reliable top 3 team.