Itemize Backend Developer interview questions

I had a short phone interview with a frontend developer for a backend role and was then emailed an assignment to design a simple CRUD app in preferably Java. I was supplied a bunch of user data with no details of what it was intended for or how it was to be associated with any request or response payloads. I attempted to reach out to them to clarify some of my questions about the assignment and received no response. After a few days I submitted my code and received an email in less than 12 hours with their decision to not move forward with my candidacy and no explanation. I understand I can't always expect an explanation for a declined position, but the whole thing gave the impression of sloppy with lack of focus and rude that my code wasn't truly reviewed or considered based on the elapsed response time after submission.