I don't believe it is a sexual "addiction"-- more on the lines of a disorder(due to faulty thinking, anxiety, depression and the like), but with that said....
The way I understand it is that Narcissists do things from their own view point, their own feelings, with little to no regard of what that will do to others in their lives. -- which is how some with sexual disorder think. Also, from what I understand they(narcissists) have a huge sense of entitlement.--- which could be how some people struggling with sexual disorder think.

I struggle to understand how a behavior and/or dysfunctional thought is deemed an addiction... and not an obsession or compulsion.
I truly do not see how such can be considered an addiction.

do you know if "cutting" (self injury) is considered an addiction? that seems to be similar to the sexual disorder... they both are behaviors to stave off an uncomfortable feeling or to feel something that one isn't able to without it.