... that most of the ethno-nationalists in America who refer to themselves as "European" are about as "European" as Rachel Dolezal is "African American."
That is, they want to be "European" and they think of themselves as "European," but they're not "European."
They were born in America, not in Europe (less than 14% of Americans were born abroad, let alone in Europe, and it's likely that a lower percentage of those are "European ethno-nationalists" than is the case in the general population).
There's a very good chance that their parents were born in America, not in Europe.
There's a reasonably good chance that their grandparents were born in America, not in Europe.
Sure, some of their genes may trace back to European ancestors. But all of their genes trace back to African ancestors, and they're not running around calling themselves "African."
If you were born in America, likely to American parents, and raised to adulthood in America, you're not "European," you're "American."