Urie went to the back of the arena to wait for his turn when he noticed that a familiar man was walking towards the ring where a battle just ended.
He carefully followed the silhouette of the man until he noticed that the man was the one who they encountered yesterday when they registered. It was Xeno.
It seems that the man didn't notice him as he went straight towards the ring. A few moments after Xeno entered, Urie was called by an NPC staff member to enter the ring that just finished the battle.
The stadium was not that crowded, because it was only the qualifiers, meaning the thrill of a fight was not there yet, though some people were already watching the fight to get some detail about the contestants.
Those people were the one that were preparing to make a betting session during the tournament.
Although it's not illegal to do it, the system would recognize it as an illegal act if it wasn't registered as a side event in the tournament.