The thing is, many of those laws still existed in other areas of Europe. Hence the "Ghettos" of countries like Poland. Laws and institutions like that had died off in Germany because of the Kaiser. Hitler simply used Jim Crowe to find a way to bring them back into a "Modern Democracy".
That was hardly unique. A great many in that era believed the Indians to be the "Lost Tribe" of Israel. To the Mormons, they are the Lamanites.
A lot of Europeans looked at the more "European" facial features of the East Coast Indians, and believed them to be descendants of voyagers from across the Atlantic. Look at pictures and drawings of say Mohawk or other Eastern tribes, they look much more European than those from say the Penutian or West Coast tribes.
You even have some debating this even today, as you have the "Asia Immigration Only" believers, trying to suppress any data collected that support the Solutreans theory (that the immigration came in both directions, with the European being earlier, but the Asian being larger). Even though increasingly we are finding ancient roots of Soultrean DNA has it's roots in Europe. But because of politicization, many try to pass it off as either early groups that went all the way from Europe to America through Asia, or even co-evolution of identical genetic groups.
Ignoring things like tools that existed at the earliest on the East Coast which had first been developed in Europe, and that a key genetic marker (Haplogroup R1) is almost exclusively found in Europe, and is also found in high numbers in East Coast Indians, but decreases as you move West.
Even under modern studies, the Algonquin Nation members to the Germans would likely be Aryan. But the Stillaguamish Tribe of Washington likely would not be, nor the Inuit.