If he was hanging around the group of girls, chatting or dancing etc, they may have discussed going to eat or getting a taxi or a whole host of 'later' plans.
If I went to the bathroom and a guy who I knew (even if only from that night) said - the girls said they are making their way to 'a taxi rank or pick up point', a restaurant etc, I may have left with him to meet my mates. No-one thinks that someone who acts so normally (or even a tad off in a drinking situation) is going to hurt them, and I may have felt safer walking with him to the meet point than walking alone.
All just possibilities.