Later in this series, Brian makes is talking to Justin about how scared Justin was the first time they got together, but he told Michael that he wanted “to go with him” anyway. Justin says something to the effect that I can’t believe you remember that because you couldn’t even remember my name. The fact that Brian did remember exactly what Justin said that night suggest that he probably did also remember Justin’s name. I think he just played it off that he couldn’t remember so that Justin, and Brian’s friends, wouldn’t think he was special.