¿Qué parece justificar el calificativo que le aplica su tía a Tom «demonio»?

From the text:

“But as I was saying,” said Aunt Polly, “he warn’t bad, so to say—only mischeevous. Only just giddy, and harum-scarum, you know. He warn’t any more responsible than a colt. He never meant any harm, and he was the best-hearted boy that ever was”—and she began to cry.