Albus had kept an eye on Gellert all night long. There was a tracking spell on him to make sure that he was safe (and keep him under control). He had wanted to go and talk to him, but Gellert hadn't spoken to anyone until now and deserved some time alone.
Once Tom was seen (and really Aurors were too loud), his attention was diverted. However as he turned to look back for Gellert, he couldn't find him.
He didn't know what had happened, but he would find out soon enough. He used the tracking spell and Apparated to where Gellert was. He didn't even bother with his wand, he could hurt people without, and a smile usually threw them off. When he arrived he found Gellert with a man who looked familiar and yet not. "Perhaps you should end the spell," he said pleasantly.