Fortune-telling eagle eye

In the first episode of the Three Kingdoms, why did Wang Situ say that Cao Cao was Dong Zhuo's eagle eye, but he dared to scold Dong Zhuo in front of Cao Cao at the birthday party, not afraid that Cao Cao would tell Dong Zhuo?

Wang Situ didn't believe Cao Cao at first, so he gave everyone a birthday party and didn't invite Cao Cao. Later, Cao Cao learned that he took the initiative to go to Wang Situ's house and was stopped by the janitor. Cao Cao also came here boldly and expressed his views and ideas. In order to convince everyone how much he hates Dong Zhuo and accuse Dong Zhuo of what he did in front of everyone, he now swears that he will be convinced if he has the chance. In fact, Wang Situ's birthday party was designed to punish Dong Zhuo, so he attended it.