"If I called a lamb's tail a 'leg', how many legs would that lamb have?"
"Five."
"Four. Calling a 'tail' a 'leg' doesn't make it so."
Probably-not-true anecdotes aside, National Socialism might have had elements of socialism to it, but best I can read, it wasn't anything like the primary plank of the platform. I think sibling comment's explanation of a reaction to the Communism(tm) at their door might be most reasonable to explain the naming.