By talking about Jason and Jason only. He`s the guy/wingman who only tells stories about the guy that`s been close to the girl to get instant rapport. How utterling flattering.
Artemis looked to trust him by proxis of Jason having a history to him and being brothers. But here`s another reason your expectations are sometimes off. Is Dick charismatic with it? Yes, but you can`t chalk that up to bad writting. Dick has always been more relaxed and social with people than Jason ever has. That`s consistantly part of their DNA as characters.
I mean, we all here realize by reading RATHO that Jason and Artemis first met on opposite sides of the battleground when he was "working" for Black Mask. Meanwhile, Dick comes from a friendly call and is instantly placed on the comfort zone. How on Earth to these two first impressions compare at all?