Yeah but Nazism spread via propaganda, which is what dogwhistling is a form of.

The Internet is the largest spreader of propaganda that humanity has ever seen, so it's not surprising that it helped revitalize neo-nazism and fascism is general. It also served to make satire and actual radicalized behavior harder to detect. A lot of the time, 4chan boards use this "edgy satire" format to normalize the behavior (to an extent). See: the "MAP" misinformation campaign they did and how it reinforced actual pedophilia and demonized LGBT groups