Dialpad Software Developer - Generalist interview questions

I had a very disappointing experience with these guys. I applied online. Got a call from HR where the guy said wanted to move forward with me, and then he sent my way an exercise to solve at home. So I sent the solution back after a couple of days, and then got an email saying that after reviewing my resume and experience (what?), I wasn't a fit. So to this day, I don't know whether they rejected me because of my resume/experience, or because they didn't like my solution to the problem. If it was the former, then why did they ask me to solve the exercise in the first place? Just wanted to waste my time? And if it was the latter... well, I don't think so, because even though I know I'm no super star, I know for a fact that my solution was good, efficient, and it was good code (and I did it in Python, which is what they use). The problem wasn't rocket science. Just be straight with people and stop waiting their time.