Not guilty here. I'll wait a while and see if anything shows up in moderator actions, and if not I'll unlock it again. I guess it's possible someone locked it by mistake as the lock button is just above the reply button and there is no confirmation (I've almost done it a couple of times).
Yeah I think if anyone had wanted it locked they would have posted why and there's been nothing either publicly or privately in the moderator section. It was probably just me or someone else hitting lock by mistake!