04/27/2012 AT 5:50 AM ET
“I’m not sure where his friends wandered off to, but this mystery brunette definitely had his full attention as Gerard stayed by her side the entire time he was at his table,” an onlooker tells PEOPLE. “They were flirting and dancing to the DJs.”
Although he appeared to be enjoying himself, he seemingly did so without alcohol.
“I don’t think he was drinking,” the source says. “He was carrying bottled water that he casually sipped.”
– Dahvi Shira