I sense that people don’t always understand the difference between white supremacy and, say, white nationalism. White nationalists (like the KKK) actively seek a state that enforces whiteness as part of our culture — endorsing apartheid or segregation, if not deportation of people of color. While violent racist militias are often called “white supremacists,” that’s an extreme form. White supremacy is simply the belief that white people are above other races — it can be as subtle as the widely-held belief that white people are generally smarter and have higher IQs, or less violent, than other races.
When a person writes that non-white people are not smart enough to be programmers (and yes, I’m both simplifying and paraphrasing, I realize) that is by definition white supremacy. It doesn’t make a person a Klansman, but it’s not necessary to join the Klan to indulge white supremacy.
As to Milo, his personal life is far less relevant than the agenda he helps move forward. Yes, I know he denies involvement with the alt right, but read up on his activity (the linked article below should be all you need) and it becomes clear that his denials are just posturing. He’s as much a part of this movement as Spencer.