While I don't know how exactly the SPLC arrived at their categorization, the "self-described" part is false. The 3rd paragraph of their "about" page shows:

> We also believe that whites, like all racial groups, have legitimate interests that must be defended. The defense of those interests is white advocacy. We seek to advance only those interests that we recognize and would defend for all other racial groups. We seek no advantages as whites — only the expression of preferences for our own people and culture that are taken for granted by people of other races but denied to us.

Now this paragraph may be a lie, and the SPLC may be correct that they are hateful supremacists. But they're not self-described as such. Again, I welcome evidence supporting this, but I don't feel inclined to go through their website to find it.