How did mr. Beale know that maniac didn't where he said he did?

Mr. Beale realized that Maniac didn't come from the place he claimed because he noticed inconsistencies in Maniac's story and behavior. Specifically, he observed that Maniac lacked basic knowledge about the neighborhood and its surroundings, which someone from that area would typically know. Additionally, Mr. Beale's own experiences and understanding of the community led him to question Maniac's credibility.