Not every tweet someone may see posted in some website or another comes with an "I am a White Nationalist" disclaimer, or is as well-known at Stormfront (which I suspect a lot of non-internet junkies have never heard of either).
I personally had never heard of Fuentes or that other guy until that post in this thread, and if you hadn't claimed he was a White Nationalist, I would never have known to check his Twitter feed. So someone could easily have reposted it somewhere else without having any clue that the guy was a racist.