It means that we tend to remain closed off from interpersonal socialization, because we are essentially "trapped inside our own heads," because we lack the capacity to pick up on the nonverbal cues that would allow us access to the thoughts and feelings of those around us.
While normal people are all interconnected in a web of social signals and messages, we stand apart, alone and unable to participate in that web of constant informational exchange.
So, actually, "Selfism" is perfectly appropriate. It's nothing like "selfishness." Besides, it's just a word. When you identify a specific set of recurring details that form a clear pattern, you have to call it something in order to communicate your discovery to other people, so that they can identify it when they see it, too.
I spent most of my life without a name for my differences and believe me, the rest of the human world was more than happy to give it all sorts of names of their own: stubborn, uncooperative, weird, dumb@ss, idjit, standoffish, odd, creepy, aloof, freakazoid, @$$h0le - one of my personal favorites was "emotionally ret*d."
I'll take "Autistic" over any of those.