Biacko, Zaros, Elidyr, and many other demigods guarding the cave tensed as they felt the strength of these men, but they did not cower. Biacko, being the strongest and most sensitive, sensed the strength of the enemies.
Obviously, their forces were superior, but they were more numerous, so the balance was not that unbalanced. Still, Biacko was surprised at the strength displayed by the leaders of Purgatory.
They had not arrived yet, but since they did not bother to hide their presence, they were easy to identify. There was no demigod of that strength that was not known to them.
That was the proof they needed. If they did not recognize him, it meant that they were either a hidden demigod, which was unlikely, or they were members of Purgatory. Biacko and the others knew that Purgatory had 5 leaders and 2 were dead, so they immediately concluded that the three approaching were the remaining leaders.