he's unconscious the entire time until the last moment when he opens his eyes while in the ocean and catches a glimpse of Barry. He never saw any of the other members or heard their names. How would he have known it was them, and more importantly, how would he have tracked them down?
Well he grabbed Helen’s crown which would tell him that one of the kids was the Beauty Queen, through a little digging he could probably find out who the other three were. Also keep in mind he’s a fisherman, as was Max. He could have casually steered a conversation with Max in that direction and Max could have told him??? (I have no proof of this but it’s a possibility)
Also, he's not superhuman, he would've had to come up for breath and headed to shore very shortly after. It's quite possible he overheard them arguing before they got back in the car, and I think everyone's name is used there.