As far as I know for a person to be a "shaman" or whatever title you would prefer to use, one must first have a connection to or calling by the spirits in general or of a particular pantheon. Often in classic shamanism this connection/calling occurs when one undergoes a death and rebirth journey, or else dies. Core shamanism doesn't require one to undergo this journey, and as such is pretty much what Doc described. Classic shamanism doesn't require a lineage either, however it generally requires a lineage, a death-rebirth process, and/or circumstances at one's birth, in one's physical appearance, or in one's life to be considered a shaman. There are things about the shaman that set the shaman apart from the community that is served. Core shamanism, again, doesn't require any of these "set apart" categories, but merely uses the concepts inherent in different shamanic traditions, boiled down, and treated for use by anyone, be they atheistic, Christian, pagan, etc. Classic shamanism tends to ride on one pantheon or to use one pantheon as the main, while core shamanism tends to use all pantheon's equally and not so much care for the tradition.
Personally, I don't consider core shamans shamans, as they don't have the calling/connection that I consider necessary in order to function as a shaman.