I just figured that it was a flub in the writing, acting, and/or direction that nobody caught, just as it happens in many, many TV shows and movies (Trek and otherwise) anyway.
This always puzzles me. Such a scene involves so many people and they do several takes. The actors alone: Sulu, the yellowshirt, the redshirt, the strange voice guy, Kirk, then the director, etc... Nobody notices that this piece of dialogue makes no sense?
What annoys me more is Sulu's "We're 200,000 kilometers from Earth." When exactly was he going to hit the brakes? And then when they cut to the exterior shots, they are in a close Moon orbit, which is a lot farther away.
I guess there are "flubs" in the entire film.