Stupidity: In the scene where Lewis and Clark nearly hit the Event Horizon, One of the crew is calling out the closing distance and another confirms this information. Regardless of clouds obscuring their view they were aware of their proximity and the fact that they were speeding towards it and forced to attempt an abrupt stop makes no sense.
Stupidity: After pushing the button for the outer door in the airlock, Justin was brought out of his trance. The door was on a delay, so why didn't he just go to the console and abort the door's opening?
Chosen answer: The movie never explicitly says; but science is as yet unsure what happens to a given piece of matter once it crosses a black hole's event horizon, so who knows? The ship could have been thrown seven years forward in time, or far enough away that it took seven years for it to drift close to Neptune. Pick any explanation you like.
The theory that the film is a stealth prequel to the 'Warhammer 40,000' universe has been confirmed by one of the writers, who was a big fan of 40K and said that the setting influenced his writing "either consciously or subconsciously" – because Games Workshop is litigious. But since the Horizon entered into the Warp, time there flows extremely differently from time in real space; while it was seven years for people in real space, it could have been seconds, or thousands of years, for the ship.