"The Scarlet Ibis" is not a true story or reflective of real people in Hurst's life. In an interview, he said that he wrote the story in reaction to a failed singing career he pursued. It's hard to understand the unusual connection between the story and Hurst's failure as a singer. Perhaps Doodle's disabilities represent Hurst's inability to make it as a singer. Even though he tried, like Doodle, he fails in the end. Like Doodle and the scarlet ibis, Hurst might have felt unappreciated for what talent he did have.
This is all speculation on my part, and just my attempt to make sense of why, according to Hurst, he wrote the story. Don't take these ideas as the definitive truth! It's interesting to think about, though.