Didn't this happen in a World Series game?? It was because of the hammer strike confusion that the new mechanic came into being.
The proper mechanic on a swinging dropped third strike is point out to the side while saying, "strike 3" and then signaling a safe mechanic while saying, "no catch". This lessens any confusion on anyone's part: the runner, the catcher, and any dumb rat.
Use the hammer on strike 1,2, and swing caught strike 3.