To speak for Billy, he's absolutely saying that, because that's exactly what the rules state. How people and areas expect that to be called is another matter.

If I would call it when the player has the foot on the court in the key, why wouldn't I call it if they lift the foot above that spot. By rule, the player hasn't left the key until both feet touch the floor outside the key.

Part of why the 3-second rule was written that way was to address a player who is gaining an advantage by having one foot outside of the lane but with the other well into the key. They can't simply lift the foot to avoid the count, they must move their body out of the key area (as demonstrated by both feet touching out).

I think you misunderstood my complaint about Billy's wording.
No you wouldn't call this, you'd keep counting and call three seconds when you got to three (or 4 or 5 depending on your personal style :D).
The wording of the sentence implies that it is a violation to life one foot out of the key. It is not a violation. It simply doesn't get the count to stop.

Who Are The Mythbusters Gonna Call ???
 

youngump: Thanks for pointing this out. The part that you quoted is actually a recent (1/1/13) addition to the List Of Misunderstood Rules. I believe that I added it after reading a thread on the Forum about three seconds. Now that I read it more carefully, it's most certainly poorly worded, and I have changed the wording:

The intent of the three-second rule is to not allow an offensive player in the lane to gain an advantage. There is no three-second count between the release of a shot and the control of a rebound, at which time a new count starts. There is no three-second count during a throwin. There is no three-second count while the ball is in the backcourt. There is a three-second count during an interrupted dribble. There is a three-second count while an offensive player has one foot in the lane and one foot outside of the lane, and the three-second count continues if this player lifts the foot in the lane so that neither foot is touching inside the lane. To stop the count this player must have both feet touch the court outside of the lane. It’s a violation for a player to step out of bounds in an attempt to avoid a three second violation. Allowance shall be made for a player who, having been in the restricted area for less than three seconds, dribbles in or moves immediately to try for goal.

youngump: Great suggestion to improve the Misunderstood Rules list. Congratulations. You are now an official Mythbuster. You will soon be receiving your official Mythbuster badge, and your official Mythbuster decoder ring.