The body must also be large enough to clear other bodies in the same orbit, except at the Trojan positions (L4 and L5), to be considered as a planet. Otherwise it would just be a Trans-Neptunian Object (TNO) or a Kuiper Belt Object (KBO) at these distances.
It obviously does in this case. But this pedantic detail is rather important. It was used to demote Pluto a few years back.