how is Bob Ewells rasist in chapter 27 (page 275)

Helen Robinson has been working on the property of Mr. Link Deas, but walks nearly a mile out of her way in order to avoid walking past the Ewell's house, because they "chunk" at her when she passes by. When Mr. Link Deas finds out, he approaches the Ewell house and yells to them, warning them not to bother Helen, or else he'll have them put in jail. The next day, Mr. Ewell follows Helen to work, "crooning foul words" the entire way, but Mr. Link Deas again threatens him with jail and he stops this behavior.