In "The Boy Who Drew Cats," why did the boy choose a small place to sleep?

Before the priest sends the boy from the temple, he gives him one last piece of advice. The priest tells the boy that he should, “Avoid large places at night—keep to small.” The boy doesn’t quite understand what the priest means.
Nonetheless, the boy trusts the priest, and so when it is time to go to sleep, and he finds himself in another temple, the boy remembers the priest’s advice and finds a “little cabinet” to sleep in. During the night, the boy hears terrible noises in the temple, and when he leaves the cabinet in the morning, he sees that the floors are “covered with blood.”
In the middle of the floor there is a huge “goblin-rat.” He supposes that the rat must have been killed by the cats he drew the previous night. He also recalls, with gratitude, the priest’s advice to “keep to small” places. The implication is that the priest knew that there were dangers lurking in the night and thus advised the boy to stay somewhere small to be better protected. This, of course, turned out to be life-saving advice.