*How to Play a Bridge Hand*, and I am confused by his description of this hand (p10, in the section "To Finesse, or to Play for the Drop"):

Root writes: "You cash the ace and king and the jack does not fall. Then you lead toward dummy's queen-ten and West follows with a low card. Since the opponents began with only six cards, the odds are slightly in favor that East has the jack; so playing the queen offers a better chance than the finesse."

Why are the odds slightly in favor that East has the jack?

Is it because, if you West plays low, there are now 5 outstanding cards, of which one must be the jack? But, not knowing the distribution, how can we say the odds are still over 50% for East to have the jack?