That is half of the criteria the IAU decided defined a planet. The problem is that our moon is rounded by its own gravity and would be classified as a planet un

That is half of the criteria the IAU decided defined a planet. The problem is that our moon is rounded by its own gravity and would be classified as a planet under that just criterion. The other half is meant to exclude moons from the 'planet' definition: the body must 'clear' the neighborhood around its orbit. The Earth is in the same solar orbit as our moon but is much more massive, thus our moon doesn't count as a planet. Pluto doesn't meet this criterion because its orbit intersects with Neptune's orbit, and Neptune is much more massive.