That simply has to do with the way that website classifies terrorist groups. It appears they use the most specific classifications possible, which is great. However, that doesn't mean there aren't reasons to examine whether those categories of terrorism fall under a larger category of right wing terrorism. Nazism is a form of fascism and fascism is a far right wing ideology. Therefore, it would make sense to call it right-wing terrorism. White extremism is a little more nebulous, but for those that identify as white nationalists, it would be totally reasonable to say that they are far-right.