The moment that they heard the explosion, they certainly understood that something bad had happened. Additionally, it had been quite a while, and they had not seen the leader of the monster tide.
At this moment, they all instinctively thought, that explosion was caused by the leader of the monster tide. And as if to prove that, the city Lord suddenly received information from the other side, telling him that there was a huge monster at the peak stage of the nine star rank that was attacking.
Considering that other than Austin and the City Lord, there was no any other person that was in the peak stage of the nine star rank. And since all of them were in the same place, it indicated that the other sides of the city were weak.
Additionally, it was clear that this monster was extremely intelligent. It had attacked the weakest side of the city, instead of coming from the direction that it was expected to be coming from.