@rizuna in the conversation that she had with Dan-I on the roof they didn't say that she was the one who created the cafe. So, she assumed that he only listened to that conversation without any prior knowledge of this matter is her doing. That is why she asked Ju-In to not tell Ji-Ho about it...
@katanyal no I think the thought of someone using her name and birthday as a username crossed her mind, so she didn't pay much attention to the meaning of the username.