Basically, the Moderator generally only votes if his vote would change the outcome. (Since if it wouldn’t change the outcome, there’s no point in making an appearance of being non-neutral on a vote, since the Moderator should moderate impartially.) But, the Moderator is a registered voter just like everyone else, with just as much of a say.
In this case, since the motion required a ⅔ vote to pass (meaning the number of Yes votes must be at least two times the number of No votes), and it would have been 85-42 without my vote (and would have passed), I voted No, making it 85-43 and thus not passing. Now, it failed because 43 voters in the room voted No, not just because I voted No. Any person changing their vote could have swayed it in either direction. But because I’m in the front of the room, it becomes news that I voted.