Do you think people really believe that Moshe is lying to them?

No, I think that they chose to believe that Moche was exaggerating. I think chose is the operative word here. There is some grey area between lying and exaggerating. Wiesel clearly felt the Jews of Singet were complacent in their own impending destruction. They were aware of ominous dangers and still decided Moche was an eccentric old man. They felt that his stories might even have truth to them but it would not affect them.