Aerith gasps, pointing a finger at Zack. "Mutual friend!"

Don't mind her, she's just excited to make the connection from Riku's vague allusion earlier.

"Hehe, I actually met him earlier. He must have gotten pushed into speed dating by one of the mascots, poor guy. He got so flustered when I suggested he was trying to find a girlfriend."

She obviously hadn't felt sorry enough for Riku to not tease him. Teasing is just her default in getting to know people.