You probably didn't submit finally, if not you'd have a "You've already responded" page in your browser history right after the questions page, sometimes google does that thing after you've clicked submit, it only reloads, and if proper care isn't taken you'd miss it, clearly, like in this case...
Damn! That's a tough one to swallow!
Most likely that's the case. Exactly same thing happened for me last season - I clicked submit and just closed the page without waiting to get confirmation that I made it. That's extremely painful thing and after it now I'm checking everything twice to be sure that my answers were submitted. I just hope that these points won't cost much in the end of season.