Far be it from me to criticise the Perfect One, but I'm afraid on this he's wrong, for two reasons:
(1) There is no absolute criterion for whether something is a planet or not - if it orbits the sun, there's grounds for calling it a planet. It's just that sometimes it's useful to us to call one thing a planet and another thing not a planet - just like there's no rigid boundary between "a small pile" and "a big heap". If you think Pluto's a planet, it's a planet.
(2) Inasmuch as these things are official, they are decided by the International Astronomical Union. And if you look at
http://www.iau.org/IAU/FAQ/PlutoPR.html you will see that the IAU officially regards Pluto as a planet. It is also officially regarded as one of a number of Trans-Neptunian Objects. In other words, being a Kuiper Belt Object and being a planet are not mutually exclusive: officially, Pluto enjoys the status of each. Perhaps if it were discovered today, we would not call it a planet, given what we know of this region of space - but that's another matter.