Short answer:
this post.
Long answer: because he doesn't post positive things about Nazis, and pokes fun at them from time to time.
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Also, everyone actually on the right understands the difference between RINOS, conservatives, reactionaries, the dead-for-years alt-right, and the tiny segment of unironic neo-Nazis. Stonetoss is reactionary; he's mocking radical progressives, liberal policies, and hypocrites across the whole political spectrum. That appeals to people to the left
and right of him on the right-wing spectrum. It's disingenuous to say it's a dog whistle specific to the furthest right fringe possible.