There's another one soon after: "that little farce you played with my sister - you think that could fool a Corleone?" It obviously fooled one Corleone.
The only ones who were were fooled were Fredo and Connie. Vito was on to carlo from the beginning when he told Tom to NEVER give him anything important, but to give him a living and to never discuss the family business with him. Santino was on to him, and was on his way to kill him. Michael was also on to him once he got back from Sicily, if not sooner.
