Vincent and Jules are on the elevator talking about foot massages. You can hear the elevator ding as they go up the floors. When the elevator stops they exit the stairway door not the elevator.
hmm....Well let's think: now let's say, the elevator was nearby the stairs. If this were so, then because of the camera work, it would appear Jules, and Vince are coming up from the stairs, dontcha think?
If you watch the whole scene properly you will see that they open a door to get into the elevator too. This is because it is an old building and so it has this type of elevator where you pull a door open to get in and out.
So no slip-up!