A poor signal might have prevented the message from going through, causing the app to save it as a draft so you don't lose the text.
While I cannot see the content of that specific file, search results for this type of query often point to discussions about on Android or iOS devices. If your image is a screenshot of a text conversation with a red "Draft" label, Why Your Message is a "Draft" 83ED76EE-FBE5-47AD-B6EC-269D5C15355B.png
iMessage saves drafts within the specific contact thread. You can also use third-party tools like the Drafts App to manage more complex message templates. Mysterious Draft Text Msg | DroidForums.net A poor signal might have prevented the message