After asking the waiter, Miguel came to know the reason for Maras' absence during this time.
As it turns out, he went out earlier to try and persuade the twins not to go once more. However, it had been a while and he was still not back. Even his waiter and the other workers in the tavern were already worried about his well being.
As for the unusual number of crowds present inside the tavern, Miguel also learned that they were here for Maras, or to be precise, for the twins and the location of that site that they had discovered.
Apparently, their description of the site made the others realize that the site probably houses a rare treasure that no one would be able to ignore.
Considering that Maras was not back yet and with a lot of mercenaries present in the tavern, Miguel guessed that the twins must have decided to explore that passage for their own. Maras must have gone to help or either take them back.