Sam naturally did not know the motive of the people but as you can tell he was also very experience handling situation like this and by sensing those people he could tell everyone of them had some kind of malicious intention, for a second he thought to attack them but then he decided to getting the true motive of those people and he also wanted to become sure that those people following him.
On the other hand he was also looking for those Monsters but unfortunately until now he did not find any trace of the water body near that place and nor did he noticed any grade monster in the place. So he already realized that he needed to go deeper than these and only then was he most likely able to find those Monsters and those other Epic grade Monsters.
