Yes it was just bad luck for you today. I understand how annoying that is. The most likely cause is speeding through. If you spent 15 minutes on a survey that they think should take you 25 minutes, it may DQ at the end. If you don't think this was the case, then it was probably something to do with your profile information. Poorly designed surveys will ask you for personal nformation at the end when they should have asked you at the beginning.
Yeah, I'm not sure what it was, since I definitely didn't speed.