The poem "The Lady of Shalott" shares all of the characteristics of a ballad except "dialogue". This poem doesn't involve a dialogue from any of the characters in the story. Yes, it has a story and is told by a third person. Yes, it has stanza structures. For example, the first four stanzas talk about the setting. The next stanzas describe the main character, then the story unfolds in the following stanzas. But this poem or ballad does not include a dialogue. That's what makes it different from other ballads.