Shapeshifting on the Astral isn't so difficult, for the most part. Some people find it easier than others, anyway. But changing your shape isn't the same as actually being something in essence, and I don't believe the Astral body is the soul itself, but can reflect the soul's image far easier than the physical body does, haha.
For myself, yeah, I'm one of those dragon people. It's a result of having had several past lives as a dragon, at least one of which left a very strong imprint on my soul. And to have incarnated as a dragon so many times, there's probably a good deal of draconic energy in my soul to begin with.
As I see it, the soul is the 'core' of a person, and this core might be sourced from one or more types of energy, and can be shaped through experiencing different lives, like clay in a mold. Some lives leave deeper, more permanent impressions than others for various reasons. The physical and astral bodies are merely the vessels or 'molds' for the soul.