Just for clarification:
This was not pre-emptive action by a Moderator. We are often asked by Calvin Lin who is affiliated with Billiant.org to lock questions that are part of ongoing contests. This is one of those cases.
That said, I wasn't the one who handled that flag. Generally I would (and I expect the other mods too) double check to see that the question is in fact a live contest question before locking. Sometimes the organisers make it easy (specific link provided to specific question on their web page). Sometimes they don't. But for the flags that I have handled concerning contest questions, I have yet to come across a flag on a question from non-current contests (excepting the Project Euler ones, which raised quite some discussion before).
Lastly, we generally do try to make sure that whenever contest questions are locked, we include a moderator message up top that states which contest it is from and when the contest end-date is. For short-term contests usually we can make sure the lock expires after the end-date. For longer-term ones sometimes it is difficult, including an end-date ensures that users who see a question we forgot to unlock can ping us to do so. Michael probably just forgot to do it this time. I'll ping him about it.
