Actually the inner rocky planets formed similarly to the outer gas ones except that the inner ones were close enough to the sun for most of their lighter material—hydrogen and helium—to be forced outward during the sun’s T-Tauri phase of high solar winds. Otherwise, they all formed as small planetesimals coalescing into larger ones until there was no more raw material in their general orbits. There are regions of instability, however, where this process remained incomplete. Namely the asteroid belt and the later discovered Kuiper belt, of which Pluto is part.
Personally I’m not particularly worried about what “defines” a planet. Naming conventions are by nature often ambiguous to a degree, resulting in exceptions to the rule. There is no real difference between a mountain and a hill, for example, except some arbitrary height from base to summit. Originally, the term “planet” referred to a star that wanders instead of remains fixed. So under that definition, the earth isn’t even a planet.
Thanks, the similarity of the process is what you obviously see, just have some problem with the materials used. There's no more reason to separate Pluto and planets further out than there is to separate the gas giants from the terrestrial planets.