“The spacecraft does so by looking for the dimming that occurs when a world transits or moves in front of a star.”
So, this means that they must have statistics that indicate what percentage of stars have a planetary elliptic that is aligned properly with our star. Unless the elliptic is oriented edge-on with us, not a single ‘world’ orbiting that star would ever transit or move in front of that star (between us and the star).
hmmm....
That is an interesting question. The spacecraft is not in earth orbit, but in a trailing solar orbit. But still, the orientation would need to be as you describe for it (an exoplanet) to obscure the view irrespective of the spacecraft's orbit relative to earth.
Wiki's article on Kepler says that the observed star systems are the ones that are on a similar galactic plane as ours - maybe that makes a difference - same plane, same orientation? I don't know. Where's Neil deGrasse Tyson when you need him?