Why is Boo blamed for the childhood accident

According to Miss. Staphanie, Boo is blamed because he "drove" the scissors into his father's leg.

According to Miss Stephanie, Boo was sitting in the livingroom cutting some items from The Maycomb Tribune to paste in his scrapbook. His father entered the room. As Mr. Radley passed by, Boo drove the scissors into his parent’s leg, pulled them out, wiped them on his pants, and resumed his activities.

Mrs. Radley ran screaming into the street that Arthur was killing them all, but when the sheriff arrived he found Boo still sitting in the livingroom, cutting up the Tribune. He was thirty-three years old then.