Otis was eager to deliver the news that the guards had left the village, but was still trying to be extra safe.
Instead of leaving, he returned to the village and continued to explore the surroundings.
'Heh, most of the guards are really gone now.' Otis laughed silently. Along the way, he only spotted one or two guards, but they were all at specific locations. To ensure that they weren't patrolling anywhere else, he waited for 15 minutes, and the guards hadn't even moved from their position.
Essentially this meant that these guards were guarding something important and would not be elsewhere.
For the guards to act in such a way, Otis was positive that whatever was inside the building must be extremely valuable. Thus, he walked away and began jotting down the notes.
These were all important information that he required to deliver to Melvin to execute the second phase of the plan.