The uniqueness of Ray Bradbury's first story could lie in its origin. It was the product of a young, budding writer's mind. It might have had a sense of urgency and a certain rawness in its execution. Maybe it was told from a very personal point of view that was different from what was common in the literature of that era. It could have had characters or situations that were not typical, and these elements combined to make it stand out as a unique piece of early work from a writer who would go on to be a legend.
One aspect that might have made Ray Bradbury's first story unique was his fresh perspective. As a new writer, he brought a new voice to the literary scene. His first story was likely full of the raw creativity that he had yet to refine, which set it apart from more established works at the time.
Ray Bradbury's first story was unique in that it was the first manifestation of his unique brand of storytelling. It may have had a naivete and a sense of discovery that his later, more polished works didn't have. It could have had a different pacing or a more experimental use of language, as he was still finding his feet as a writer. Also, it might have contained the seeds of the themes that would become his trademarks, such as the relationship between man and technology or the power of the imagination, but presented in a more embryonic form.