I suppose it could make sense, in a way....

It depends on how a planet is defined. Not being an astronomer, I have no idea - in fact is a "planet" defined in any way?

But it can't be because it's an object that orbits the sun, 'cos all the asteroids (and comets if it comes to that) also orbit the sun.

And Pluto is very small. Exactly how small compared with some of the asteroids and/or moons of Jupiter I also don't know, but possibly smaller or less mass than some of the "great moons"?.

Just some food (green cheese?) for thought..

Cheers,
Diolma