Best as I can figure (& historians still debate this) Nazi racial "science" derived from mid 19th century antisemitism & social Darwinism. The Nazis elaborated by adding so called Nordic or Aryan qualities as those they wished to promote. That left a whole lot of folks out in the cold. Even today, in the US, most white supremacist types don't necessarily rail against Slavs or Mediterranean people or Roma, but they almost never include them in their ranks, either.

What's this got to do with Jews? Rather than just view us as Untermenschen along with the above, I think it was Hitler's own personal Jew hatred, blended into National Socialism, that created the drive to render Europe Judenrein & the Holocaust.

Bottom line, as far as the Nazis were concerned Jews weren't white, & this rendered us vulnerable to Hitler's own brand of exterminationist Jew-hatred.